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Upyo changelog ​

Version 0.6.0 ​

To be released.

@upyo/core ​

  • Added Blob and replayable async content factories for attachments, with readAttachmentContent() and iterateAttachmentContent() helpers. createMessage() now retains File content without reading it; use the helpers instead of awaiting attachment.content directly. [#56, #59]
  • Added a calendar field to Message and createMessage(), which carries an iCalendar object so that a transport can compose the text/calendar part that makes a message a meeting invitation, a reply, or a cancellation. The method is read from the object's own METHOD property; passing method asserts what that property says rather than supplying it, and content that is not a single well-formed VCALENDAR object declaring exactly one supported method is rejected with a TypeError. Every content line is checked for valid names, parameters, and value characters; property-specific value syntax and scheduling requirements remain the caller's responsibility. Line endings are normalized to CRLF. [#63, #69, #70, #71]
  • Added the @upyo/core/calendar module, with the CalendarMethod, CalendarContent, and CalendarConstructor types and the parseCalendarMethod(), resolveCalendarContent(), and createCalendarAttachment() functions. [#63, #69]
  • Added messageId, date, inReplyTo, and references fields to Message and createMessage(), so that an application can choose the outgoing message identifier, store it, and correlate a reply that arrives with a matching In-Reply-To. The identifiers are held without their enclosing angle brackets, which createMessage() strips when they are supplied, and an invalid one is rejected with a TypeError. For inReplyTo and references, leaving the field unset defers to an In-Reply-To or References header supplied through headers, while an empty array suppresses it. [#58, #61]
  • Added the @upyo/core/message-id module, with generateMessageId(), parseMessageId(), formatMessageId(), and resolveThreadingHeaders(). [#58, #61]
  • Clarified that Receipt.messageId is the delivery handle a transport or a provider reports back, which is not the RFC 5322 Message-ID the message carries. [#58, #61]
  • Added support for internationalized mailbox addresses, including UTF-8 local parts and Unicode domains, to parseAddress() and createMessage(). [#45, #50]
  • Added the optional RawTransport interface and replayable RawMessage types for delivering serialized MIME with an explicit envelope. Raw sources support incremental validation and cancellation. An explicit 8bit encoding requires the caller to guarantee ASCII headers in nested MIME parts, which Upyo does not parse. [#64, #72]
  • Added the optional VerifiableTransport interface and isVerifiableTransport() type guard for checking transport configuration without sending a message. [#67, #73]

@upyo/jmap ​

  • A message carrying calendar is now composed with a text/calendar body part carrying the method parameter. [#63, #69]
  • Added JmapTransport.sendRaw() to stream serialized MIME through blob upload, import, and submission with an explicit envelope. Raw mutations are not retried automatically; uncertain submission outcomes are reported as non-retryable to prevent duplicate delivery. HTTP failures retain their status, retry delay, and response details; authentication rejections are non-retryable even without a JMAP error body. [#64, #72]
  • Added JmapTransport.verify() to check live session, account, drafts mailbox, and identity settings without sending mail or changing the session cache. Verification rejects on failure and bounds each discovery operation, including response bodies and retries, by the configured timeout. [#67, #73]
  • Fixed cancellation during JMAP retry delays so cancelled requests stop waiting immediately.
  • Added support for Blob and replayable async attachment factories, including cancellation while reading their content. Provider payloads remain buffered in memory. [#56, #59]
  • Added support for the messageId, date, inReplyTo, and references fields of Message, which map onto the messageId, sentAt, inReplyTo, and references properties of the JMAP Email object. A raw header of the same name is dropped when the corresponding field is set, since RFC 8621 §4.6 forbids two properties representing one header field. [#58, #61]
  • Fixed Email/set creating an email with the headers property, which RFC 8621 §4.6 forbids on create; each header field is now written as an individual header: property. Custom headers that duplicate a structured property, including Bcc and any Content-* field, are no longer sent, and a header value containing a carriage return or line feed is rejected. Breaking: JmapEmailCreate no longer has a headers property. [#58, #61]
  • Fixed an empty text or html body being dropped from the composed message. A body the caller supplied as an empty string is now sent as an empty part, the way @upyo/smtp composes it, rather than omitted. [#69]

@upyo/lettermint ​

  • A message carrying calendar now sends the iCalendar object as an invite.ics attachment whose content type keeps the method parameter, ahead of the message's own attachments. This transport cannot compose a text/calendar body alternative, so the scheduling semantics are not guaranteed to survive; see the documentation on calendar invitations. [#63, #69]
  • Added support for Blob and replayable async attachment factories, including cancellation while reading their content. Provider payloads remain buffered in memory. [#56, #59]
  • Added support for the inReplyTo and references fields of Message, which are sent as custom headers. A field left unset defers to an In-Reply-To or References header supplied through headers, and an empty array suppresses it. messageId and date are not sent, because the provider does not document whether a supplied value survives. [#58, #61]

@upyo/logtape ​

  • Added LogTape observability transport. [#33]

    • Added LogTapeTransport class for logging email delivery lifecycle events with configurable categories and levels.
    • Supports log-only development use and decorating another transport without changing its receipts or errors.
    • Supports optional full-message recording as structured properties or as development-friendly logs with inline subjects and bodies.
    • Supports streaming sendMany(), AbortSignal cancellation, and wrapped transport disposal.

@upyo/maileroo ​

  • A message carrying calendar now sends the iCalendar object as an invite.ics attachment whose content type keeps the method parameter, ahead of the message's own attachments. This transport cannot compose a text/calendar body alternative, so the scheduling semantics are not guaranteed to survive; see the documentation on calendar invitations. [#63, #69]

  • Added Maileroo transport. [#30, #31]

  • Added support for Blob and replayable async attachment factories, including cancellation while reading their content. Provider payloads remain buffered in memory. [#56, #59]

  • Added support for the inReplyTo and references fields of Message, which are sent as custom headers. A field left unset defers to an In-Reply-To or References header supplied through headers, and an empty array suppresses it. messageId and date are not sent, because the provider does not document whether a supplied value survives. [#58, #61]

@upyo/mailgun ​

  • A message carrying calendar now sends the iCalendar object as an invite.ics attachment whose content type keeps the method parameter, ahead of the message's own attachments. This transport cannot compose a text/calendar body alternative, so the scheduling semantics are not guaranteed to survive; see the documentation on calendar invitations. [#63, #69]
  • Added support for Blob and replayable async attachment factories, including cancellation while reading their content. Provider payloads remain buffered in memory. [#56, #59]
  • Added support for the inReplyTo and references fields of Message, which are sent as custom headers. A field left unset defers to an In-Reply-To or References header supplied through headers, and an empty array suppresses it. messageId and date are not sent, because the provider does not document whether a supplied value survives. [#58, #61]

@upyo/mailtrap ​

  • A message carrying calendar now sends the iCalendar object as an invite.ics attachment whose content type keeps the method parameter, ahead of the message's own attachments. This transport cannot compose a text/calendar body alternative, so the scheduling semantics are not guaranteed to survive; see the documentation on calendar invitations. [#63, #69]

  • Added Mailtrap transport. [#32 by Narek Hovhannisyan]

  • Added support for Blob and replayable async attachment factories, including cancellation while reading their content. Provider payloads remain buffered in memory. [#56, #59]

  • Added support for the inReplyTo and references fields of Message, which are sent as custom headers. A field left unset defers to an In-Reply-To or References header supplied through headers, and an empty array suppresses it. messageId and date are not sent, because the provider does not document whether a supplied value survives. [#58, #61]

@upyo/opentelemetry ​

  • Fixed the email.content.type span attribute and the content_type metric label, which reported text or html for a message carrying a calendar. Such a message is multipart on every transport, either as a text/calendar alternative or as an invite.ics attachment, and is now labelled multipart. [#69]
  • Fixed the estimated message size reported on a span and in the email.message.size histogram, which counted UTF-16 code units rather than the bytes it claimed. A subject or body outside Basic Latin was undercounted, a Korean one by roughly two thirds. [#69]
  • The estimated message size reported on a span now includes the calendar payload. [#63, #69]

@upyo/plunk ​

  • A message carrying calendar now sends the iCalendar object as an invite.ics attachment whose content type keeps the method parameter, ahead of the message's own attachments. This transport cannot compose a text/calendar body alternative, so the scheduling semantics are not guaranteed to survive; see the documentation on calendar invitations. [#63, #69]
  • A calendar message that would exceed the limit of five attachments is now rejected with a RangeError, rather than silently dropping one of the message's own files to make room for the invitation. [#63, #69]
  • Added support for Blob and replayable async attachment factories. Attachment reads remain buffered, and failed reads still omit the attachment; caller cancellation now aborts the send instead. [#56, #59]
  • Added support for the inReplyTo and references fields of Message, which are sent as custom headers. A field left unset defers to an In-Reply-To or References header supplied through headers, and an empty array suppresses it. messageId and date are not sent, because the provider does not document whether a supplied value survives. [#58, #61]

@upyo/resend ​

  • A message carrying calendar now sends the iCalendar object as an invite.ics attachment whose content type keeps the method parameter, ahead of the message's own attachments. This transport cannot compose a text/calendar body alternative, so the scheduling semantics are not guaranteed to survive; see the documentation on calendar invitations. [#63, #69]
  • A calendar message is now sent individually rather than through the batch API, which accepts no attachments. [#63, #69]
  • Added support for Blob and replayable async attachment factories, including cancellation while reading their content. Provider payloads remain buffered in memory. [#56, #59]
  • Added support for the inReplyTo and references fields of Message, which are sent as custom headers. A field left unset defers to an In-Reply-To or References header supplied through headers, and an empty array suppresses it. messageId and date are not sent, because the provider does not document whether a supplied value survives. [#58, #61]
  • Fixed incorrect Base64 padding that corrupted attachment contents. [#59]

@upyo/sendgrid ​

  • A message carrying calendar now sends the iCalendar object as an invite.ics attachment whose content type keeps the method parameter, ahead of the message's own attachments. This transport cannot compose a text/calendar body alternative, so the scheduling semantics are not guaranteed to survive; see the documentation on calendar invitations. [#63, #69]
  • Added support for Blob and replayable async attachment factories, including cancellation while reading their content. Provider payloads remain buffered in memory. [#56, #59]
  • Added support for the inReplyTo and references fields of Message, which are sent as custom headers. A field left unset defers to an In-Reply-To or References header supplied through headers, and an empty array suppresses it. messageId and date are not sent, because the provider does not document whether a supplied value survives. [#58, #61]

@upyo/ses ​

  • A message carrying calendar now sends the iCalendar object as an invite.ics attachment whose content type keeps the method parameter, ahead of the message's own attachments. This transport cannot compose a text/calendar body alternative, so the scheduling semantics are not guaranteed to survive; see the documentation on calendar invitations. [#63, #69]
  • An attachment with no content ID no longer sends an empty ContentId field. [#63, #69]
  • Added support for Blob and replayable async attachment factories, including cancellation while reading their content. Provider payloads remain buffered in memory. [#56, #59]

@upyo/smtp ​

  • A message carrying calendar is now composed with a text/calendar alternative, placed after the text and HTML bodies and Base64 encoded so that the object's line structure survives unchanged. The method parameter repeats the object's own METHOD property, as RFC 6047 §2.4 requires. [#63, #69]
  • Added SMTP envelope overrides for using different MAIL FROM and RCPT TO addresses without changing the visible message headers. Overrides support null reverse-paths and per-message resolvers for bulk VERP delivery. [#52, #54]
  • Added SmtpTransport.sendRaw() for delivering serialized MIME with an explicit envelope, streaming validation, DSN, and cancellation. Raw sends preserve existing headers and signatures and bypass configured DKIM signing. [#64, #72]
  • Added SmtpTransport.verify() to check a fresh connection, TLS policy, and configured authentication without sending mail. Verification shares the connection limit, closes its connection afterward, and rejects on failure. SmtpResponseError and SmtpAuthResponseError are now exported for inspecting server replies. [#67, #73]
  • Fixed cancellation during SMTP connection setup and while waiting for a custom OAuth2 token provider, so cancelled operations release their connections promptly.
  • Added automatic SMTPUTF8 delivery for internationalized sender, recipient, and reply-to addresses. Servers must advertise SMTPUTF8 and 8BITMIME; unsupported sends fail without starting a mail transaction. [#45, #50]
  • Added incremental SMTP attachment encoding and backpressured DATA writes. Set dkim.bodyMode to "streaming" for bounded attachment memory with two source reads, or keep the default "buffered" mode for one read. Changed replay content fails with smtp.attachment-replay-mismatch before acceptance. Source inactivity and size-limit failures close unfinished DATA connections. [#56, #59]
  • Added structured enhanced status codes to SMTP delivery failures. Valid RFC 2034 reply prefixes expose their class, subject, and detail while preserving the server's original text; address, content, and network statuses also receive more specific error categories. [#46, #51]
  • Added support for the messageId, date, inReplyTo, and references fields of Message. Each takes precedence over the matching Message-ID, Date, In-Reply-To, or References header, which still applies when the field is left unset. [#58, #61]
  • Changed the generated Message-ID to use the sender's domain instead of the fixed upyo.local, which RFC 6762 reserves for multicast DNS. [#58, #61]
  • Fixed the Date header ending in the obsolete GMT zone rather than the numeric +0000 RFC 5322 §3.3 asks for. [#58, #61]
  • Fixed SMTPUTF8 not being negotiated for a non-ASCII value in a header field written verbatim, such as a Message-ID supplied as a custom header. [#58, #61]
  • Changed In-Reply-To and References supplied as custom headers to be written verbatim rather than RFC 2047 encoded, since both carry structured values that the encoding made invalid. A non-ASCII value in one therefore now requires a server that advertises SMTPUTF8, and a value containing a carriage return or line feed is rejected instead of being neutralized by the encoding. [#58, #61]
  • Added the requireTls configuration option. When enabled for a plaintext connection, the transport issues STARTTLS even if the server does not advertise it and fails delivery unless the TLS upgrade succeeds. The option defaults to false; the existing protection against cleartext authentication to non-loopback hosts remains in effect. STARTTLS on Deno requires Deno 2.7.13 or later.
  • Fixed connection pooling when pool is omitted so that the documented default of true takes effect. Dispose the transport with await using or call closeAllConnections() to release pooled connections when finished.
  • Reduced SMTP round trips by sending MAIL FROM and all RCPT TO commands together when the server advertises the PIPELINING extension. Replies, including multiline replies, remain associated with their commands and rejected recipients in server response order. [#42, #47]
  • Added support for the SMTP SIZE extension. The transport declares each encoded message's size on MAIL FROM and returns a failed receipt before uploading messages that exceed an advertised fixed maximum. Bare SIZE and SIZE 0 advertisements continue without a local limit. [#43, #48]
  • Added SMTP delivery status notification requests through the RFC 3461 DSN extension. Per-message RET and ENVID options and per-recipient NOTIFY and ORCPT options are validated and serialized on the SMTP envelope. Requests fail before MAIL FROM when the server does not advertise DSN. [#44, #49]
  • Fixed DKIM signatures using ed25519-sha256 or simple header canonicalization failing verification by receiving mail servers.
  • Fixed SMTP connections to infer the secure default from the port. Port 465 uses implicit TLS; all other ports start with plaintext and upgrade with STARTTLS when advertised. Set secure: true explicitly to use implicit TLS on a nonstandard port. [#53, #55]

Version 0.5.6 ​

Released on September 9, 2026.

@upyo/smtp ​

  • Fixed closeAllConnections() and async disposal leaving connections open when sends were still in progress. Shutdown now waits for previously started sends, including those waiting for a connection, and closes their connections instead of returning them to the pool. New sends wait until shutdown completes, after which the transport can be reused. Finish or return any started sendMany() iteration before awaiting shutdown. [#66]

  • Added regression coverage for the sendMany() connection cleanup fix introduced in 0.5.5. Breaking out of the iteration releases the connection without sending the remaining messages, with pooling enabled or disabled and with synchronous or asynchronous message sources. [#65]

Version 0.5.5 ​

Released on September 8, 2026.

@upyo/smtp ​

  • SmtpConfig.poolSize is now enforced as a hard limit on how many connections one transport may have open at the same time. Concurrent send() and sendMany() calls used to open a connection each, so a transport configured with poolSize: 5 could open a hundred connections for a hundred concurrent sends and trip a provider's simultaneous-connection limit. A call that arrives once the limit is reached now waits for a connection to be handed back, and cancelling it through its AbortSignal rejects without sending the message. [#62]

    The limit counts connections that are being established, connections that are currently sending, and idle connections retained for reuse, and it applies whether or not SmtpConfig.pool is enabled. Note that a sendMany() call holds its connection for the whole iteration, so running more concurrent sendMany() calls than poolSize makes the extra ones wait.

  • Fixed overlapping returns retaining more idle connections than SmtpConfig.poolSize. Returning a connection checked the pool size before awaiting RSET, so several returns could pass the check together and then all be retained. [#62]

  • Abandoning a sendMany() iteration early, such as with break, now returns its connection instead of leaving it open until the transport is disposed.

  • new SmtpTransport() now throws a RangeError when poolSize is neither a positive integer nor Infinity, rather than accepting a value that no connection could satisfy. Pass Infinity to opt out of the limit and keep the unbounded behaviour of earlier versions.

Version 0.5.4 ​

Released on September 7, 2026.

@upyo/core ​

  • createMessage() now rejects a carriage return or line feed in an address, an attachment's content type, or an attachment's content ID with a TypeError. A transport that composes the message itself writes these values into header fields as given, so either character ended the field and let the rest of the value appear as further header fields. [#60]

    Address strings were already rejected by parseAddress(), but the object form passed through unchecked, so createMessage({ to: { address: "[email protected]\r\nBcc: …" } }) forged a Bcc field. Attachments were unchecked in either form, and an uploaded file's declared content type is routinely chosen by whoever uploaded it.

    Values that arrive through a Message object built by hand rather than through createMessage() are still passed on as given.

@upyo/smtp ​

  • Stopped emitting duplicate header fields when a custom header collides with one the transport composes itself. RFC 5322 §3.6 permits at most one Date, From, Message-ID, Subject, and similar field per message, but every custom header used to be appended after the composed ones. A duplicate Content-Type was the worst case: it preceded the real one, so receivers that take the first occurrence misread the body and ignored the MIME boundaries. [#57]

    • Date and Message-ID have no counterpart on Message, so a custom header now replaces the generated default instead of adding a second field. Applications can finally choose an outgoing message identifier for reply correlation. Header names are matched case-insensitively, and the values are written verbatim rather than RFC 2047 encoded. A value containing a carriage return or line feed is rejected with a TypeError, so it cannot inject additional header fields. Messages that supply neither header keep the previous generated values.

    • Custom From, To, Cc, Bcc, Reply-To, Subject, MIME-Version, Content-Type, and Content-Transfer-Encoding headers are now ignored, because the corresponding Message fields and the MIME structure are authoritative. Set the structured fields instead. A custom Bcc header used to disclose blind recipients to everyone who received the message.

    • Custom X-Priority and X-MSMail-Priority headers are still sent for messages of normal priority, but no longer duplicate the headers derived from a high or low priority.

Version 0.5.3 ​

Released on August 27, 2026.

@upyo/smtp ​

  • Accepted 251 responses to RCPT TO, allowing delivery to continue when an SMTP server accepts responsibility for forwarding a recipient. [#37]

  • Continued SMTP delivery when at least one envelope recipient is accepted. Successful SmtpReceipt values now list rejected recipients with their reply codes, response text, and retryability so callers can detect partial delivery and retry only temporarily rejected recipients. [#38]

  • Kept multibyte UTF-8 characters within a single RFC 2047 encoded word when splitting long non-ASCII header values. [#39]

  • Folded long address, subject, custom, and attachment header fields to keep their physical lines within the RFC 5322 hard limit of 998 characters. Long attachment filenames now use RFC 2231 continuations, while a custom header token that cannot be folded produces a failed receipt instead of an invalid message. [#40]

  • Retried the SMTP greeting with HELO when a legacy server rejects EHLO as an unrecognized or unimplemented command. [#41]

Version 0.5.2 ​

Released on August 27, 2026.

@upyo/smtp ​

  • Prevented SMTP authentication from sending passwords or OAuth 2.0 access tokens over cleartext connections to non-loopback hosts. Configurations using secure: false now require a successful STARTTLS upgrade before authenticating; otherwise delivery returns a failed Receipt without transmitting credentials. Cleartext authentication to loopback hosts remains available for local development. [#36]

Version 0.5.1 ​

Released on July 16, 2026.

@upyo/plunk ​

  • Updated the default Plunk API base URL to https://next-api.useplunk.com and adapted request and response handling to the new API contract. [#35]

Version 0.5.0 ​

Released on July 1, 2026.

@upyo/core ​

  • Added structured delivery error metadata to failed Receipt values. Failed receipts still include errorMessages for existing code, and may now also include errors, retryable, provider, attempts, and timestamp fields for programmatic error handling. Structured errors may also include provider-specific providerDetails when a transport exposes them. [#25, #27]

    Receipt, ReceiptError, and Transport are now generic over the transport provider id, and Transport implementations expose a stable id field so provider metadata can be type-checked.

    • Added the ReceiptError interface.
    • Added the ReceiptErrorCategory type.
    • Added the ReceiptErrorClassification interface.
    • Added the CreateReceiptErrorOptions interface.
    • Added the CreateFailedReceiptOptions interface.
    • Added the classifyHttpStatus() function.
    • Added the classifyReceiptError() function.
    • Added the createReceiptError() function.
    • Added the createFailedReceipt() function.
    • Added the parseRetryAfter() function.

@upyo/jmap ​

  • Updated JmapTransport to return structured failure receipts with provider ids, retryability, HTTP status codes, retry delay metadata from Retry-After, and attempt counts where available. [#25, #27]

@upyo/lettermint ​

  • Added Lettermint transport. [#22, #23]

    • Added LettermintTransport class.
    • Added LettermintConfig interface.
    • Added ResolvedLettermintConfig type.
    • Added LettermintSettings interface.
    • Added LettermintApiError class.
    • Added LettermintBatchResponse type.
    • Added LettermintError interface.
    • Added LettermintResponse interface.
    • Added LettermintStatus type.
    • Supports single sends, batch sends, idempotency keys, attachments, inline images, routes, tags, metadata, and tracking settings.

@upyo/mailgun ​

  • Updated MailgunTransport to return structured failure receipts with provider ids, retryability, HTTP status codes, retry delay metadata from Retry-After, and attempt counts where available. [#25, #27]

@upyo/plunk ​

  • Updated PlunkTransport to return structured failure receipts with provider ids, retryability, HTTP status codes, retry delay metadata from Retry-After, and attempt counts where available. [#25, #27]

@upyo/resend ​

  • Updated ResendTransport to return structured failure receipts with provider ids, retryability, HTTP status codes, retry delay metadata from Retry-After, and attempt counts where available. Batch item failures now include structured error metadata as well. [#25, #27]

@upyo/sendgrid ​

  • Updated SendGridTransport to return structured failure receipts with provider ids, retryability, HTTP status codes, retry delay metadata from Retry-After, and attempt counts where available. [#25, #27]

@upyo/ses ​

  • Updated SesTransport to return structured failure receipts with provider ids, retryability, HTTP status codes, retry delay metadata from Retry-After, and attempt counts where available. [#25, #27]

@upyo/smtp ​

  • Updated SmtpTransport to return structured failure receipts with provider ids, retryability, attempt counts, and classified network, timeout, authentication, and rejection errors. [#25, #27]

  • Added OAuth 2.0 authentication support to the SMTP transport, using the SASL XOAUTH2 and OAUTHBEARER (RFC 7628) mechanisms. This enables authentication with providers such as Gmail and Outlook that require OAuth 2.0 instead of passwords. [#19, #24]

    • SmtpAuth is now a discriminated union of SmtpUserPassAuth (username/password, as before) and the OAuth 2.0 variants. Existing { user, pass } configurations continue to work unchanged.
    • Added SmtpOAuth2Auth, SmtpOAuth2TokenAuth, and SmtpOAuth2RefreshAuth interfaces, and the SmtpUserPassAuth interface.
    • Added the OAuth2TokenProvider type. The accessToken field accepts either a static token string or a callback returning a fresh token, which can integrate an external OAuth client (e.g., google-auth-library or msal-node) for transparent refresh.
    • Added the built-in refresh_token grant flow (SmtpOAuth2RefreshAuth): provide clientId, refreshToken, and tokenEndpoint, and the transport exchanges them for an access token, caching it across pooled connections until shortly before it expires.
    • Added the SmtpAuthError class, thrown on OAuth token acquisition and SASL authentication failures.

  • Changed SmtpTransport.send() and SmtpTransport.sendMany() to report connection and authentication setup failures as a failed Receipt instead of throwing. Previously, a failure to connect or authenticate (e.g., an invalid host, a refused connection, or rejected credentials) rejected the returned promise, which was inconsistent with message-level failures (such as a rejected recipient) that were already reported as a failed Receipt. Now all delivery failures—including setup failures—are reported uniformly as a failed Receipt. Cancellation via AbortSignal continues to reject. [#19, #24]

@upyo/pool ​

  • Updated PoolTransport to preserve child transport provider ids in aggregated structured errors. The pool itself reports failed aggregate receipts with the "pool" provider id, while child errors keep the underlying transport ids as a type-safe union. [#25, #27]

@upyo/retry ​

  • Added retry transport. RetryTransport wraps any existing transport and retries transient failed receipts or thrown transient errors using configurable exponential backoff, jitter, Retry-After metadata, and sendMany() launch throttling. Use it when one provider should absorb temporary rate limits, server errors, and network failures before handing a failure back to application code. [#26, #28]

@upyo/opentelemetry ​

  • Changed the built-in error category labels from underscore spelling to hyphen spelling: rate-limit, service-unavailable, and server-error. OpenTelemetry metrics now prefer structured receipt categories when a wrapped transport returns them, then fall back to the configured error classifier. [#25, #27]

Version 0.4.1 ​

Released on July 16, 2026.

@upyo/plunk ​

  • Updated the default Plunk API base URL to https://next-api.useplunk.com and adapted request and response handling to the new API contract. [#35]

Version 0.4.0 ​

Released on December 25, 2025. Happy Holidays!

@upyo/core ​

  • Added idempotencyKey property to Message interface. [#16]

    This allows users to provide their own idempotency key for request deduplication when retrying failed send operations. By including the key in the message itself, retries become simpler—just resend the same message object. If not provided, transports may generate their own key internally (behavior varies by transport implementation).

@upyo/smtp ​

  • Added DKIM (DomainKeys Identified Mail) signing support. [#18]

    Outgoing emails can now be signed with DKIM for improved deliverability and authentication. The implementation uses the standard Web Crypto API for cross-runtime compatibility (Node.js, Deno, Bun, edge functions).

    • Added DkimConfig interface for configuring DKIM signing.
    • Added DkimSignature interface for individual signature settings.
    • Added DkimAlgorithm type supporting rsa-sha256 (RFC 6376) and ed25519-sha256 (RFC 8463).
    • Added DkimCanonicalization type for header/body canonicalization.
    • Added DkimSigningFailureAction type (throw or send-unsigned).
    • Supports multiple DKIM signatures per message.
    • Configurable failure handling: throw error or send unsigned.
    • Accepts both PEM strings and CryptoKey objects for private keys.

@upyo/jmap ​

  • Added JMAP transport for sending emails via JMAP protocol. [#10]

    JMAP (JSON Meta Application Protocol) is a modern, efficient protocol for email access and submission, defined in RFC 8620 (core) and RFC 8621 (mail). This transport provides:

    • Automatic session discovery and caching
    • Automatic identity resolution from sender email
    • Bearer token authentication
    • Exponential backoff retry with configurable attempts
    • Request timeout and AbortSignal support
    • Text and HTML message content (multipart/alternative)
    • Priority headers (X-Priority, Importance)
    • Custom headers
    • File attachments via blob upload
    • Inline attachments (multipart/related)

@upyo/resend ​

  • Added support for user-provided idempotency keys via Message.idempotencyKey. [#16]

    Each message can now include an idempotencyKey to ensure it is not sent multiple times during retries. For batch operations via sendMany(), the first message's key is used for the entire batch request. If not provided, a unique key is automatically generated for each request.

Version 0.3.4 ​

Released on December 18, 2025.

@upyo/resend ​

  • Fixed idempotency key not being sent as an HTTP request header. [#16]

    The Resend transport was incorrectly adding the Idempotency-Key to the email's custom headers inside the JSON payload, but the Resend API expects it as an HTTP request header. This fix moves the idempotency key to the proper location.

Version 0.3.3 ​

Released on December 13, 2025.

@upyo/core ​

  • Fixed a potential SMTP command injection vulnerability.

    Email addresses are now validated to prevent newline characters (\r or \n), which could be used to inject malicious SMTP commands.

Version 0.3.2 ​

Released on December 12, 2025.

@upyo/ses ​

  • Fixed headers serialization issue on edge runtimes. [#15]

    The SES transport now converts the Headers object to a plain object before passing to fetch(), which resolves “Missing Authentication Token” errors on edge runtimes like Bunny CDN Edge that don't properly serialize Headers objects.

Version 0.3.1 ​

Released on November 3, 2025.

@upyo/smtp ​

  • Added STARTTLS support for secure connection upgrade. The SMTP transport now automatically detects and uses STARTTLS when connecting to servers that advertise this capability (such as Protonmail, Office 365, and others). This allows using port 587 with secure: false for automatic encryption upgrade. [#14]

Version 0.3.0 ​

Released on September 16, 2025.

@upyo/pool ​

  • Added pool transport for combining multiple email providers with load balancing and failover strategies. [#8]

    • Added PoolTransport class with AsyncDisposable support.
    • Added PoolConfig interface.
    • Added ResolvedPoolConfig type.
    • Added TransportEntry interface.
    • Added ResolvedTransportEntry type.
    • Added PoolStrategy type for built-in strategies.
    • Added Strategy interface for custom routing logic.
    • Added TransportSelection interface.
    • Added RoundRobinStrategy class for equal distribution.
    • Added WeightedStrategy class for proportional distribution.
    • Added PriorityStrategy class for failover-based routing.
    • Added SelectorBasedStrategy class for content-based routing.
    • Support for round-robin, weighted, priority, and selector-based strategies.
    • Automatic failover and retry logic with configurable limits.
    • Comprehensive error aggregation across multiple providers.

@upyo/plunk ​

  • Added Plunk transport. [#11]

    • Added PlunkTransport class.
    • Added PlunkConfig interface.
    • Added ResolvedPlunkConfig interface.
    • Added PlunkError interface.
    • Added PlunkResponse interface.
    • Support for both cloud-hosted and self-hosted Plunk instances.

@upyo/resend ​

  • Added Resend transport. [#9]

    • Added ResendTransport class.
    • Added ResendConfig interface.
    • Added ResolvedResendConfig interface.
    • Added ResendApiError interface.
    • Added ResendBatchResponse interface.
    • Added ResendError interface.
    • Added ResendResponse interface.

Version 0.2.4 ​

Released on December 13, 2025.

@upyo/core ​

  • Fixed a potential SMTP command injection vulnerability.

    Email addresses are now validated to prevent newline characters (\r or \n), which could be used to inject malicious SMTP commands.

Version 0.2.3 ​

Released on December 12, 2025.

@upyo/ses ​

  • Fixed headers serialization issue on edge runtimes. [#15]

    The SES transport now converts the Headers object to a plain object before passing to fetch(), which resolves “Missing Authentication Token” errors on edge runtimes like Bunny CDN Edge that don't properly serialize Headers objects.

Version 0.2.2 ​

Released on November 3, 2025.

@upyo/smtp ​

  • Added STARTTLS support for secure connection upgrade. The SMTP transport now automatically detects and uses STARTTLS when connecting to servers that advertise this capability (such as Protonmail, Office 365, and others). This allows using port 587 with secure: false for automatic encryption upgrade. [#14]

Version 0.2.1 ​

Released on August 4, 2025.

@upyo/smtp ​

  • Fixed “Maximum call stack size exceeded” error when sending large attachments. [#6]

    The SMTP transport now uses Buffer.from().toString('base64') instead of the legacy btoa() function for base64 encoding, which resolves stack overflow issues with large attachments (e.g., 500KB+ files).

  • Fixed UTF-8 encoding issue where email addresses were incorrectly encoded in SMTP headers. [#7]

    Only display names are now encoded using RFC 2047 encoding, while email addresses remain unencoded. For example, German ÄÖÜ <[email protected]> now correctly becomes =?UTF-8?B?...?= <[email protected]> instead of encoding the entire string including the email address.

Version 0.2.0 ​

Released on July 17, 2025.

@upyo/core ​

  • Improved type safety by making array fields readonly.

    • Changed the type of Message.recipients property from Address[] to readonly Address[].
    • Changed the type of Message.ccRecipients property from Address[] to readonly Address[].
    • Changed the type of Message.bccRecipients property from Address[] to readonly Address[].
    • Changed the type of Message.replyRecipients property from Address[] to readonly Address[].
    • Changed the type of Message.attachments property from Attachment[] to readonly Attachment[].
    • Changed the type of Message.tags property from string[] to readonly string[].

  • Enhanced email address type safety with template literal types.

    • Added EmailAddress type.
    • Changed Address.address property type from string to EmailAddress.
    • Added isEmailAddress() type guard function for runtime email validation.

@upyo/ses ​

  • Added Amazon SES transport. [#3]

    • Added SesTransport class.
    • Added SesConfig interface.
    • Added SesAuthentication interface.

@upyo/opentelemetry ​

  • Added OpenTelemetry observability support. [#5]

    • Added OpenTelemetryTransport class.
    • Added OpenTelemetryConfig interface.
    • Added ObservabilityConfig interface.
    • Added MetricsConfig interface.
    • Added TracingConfig interface.
    • Added AttributeExtractor type.
    • Added ErrorClassifier type.
    • Added createErrorClassifier() function.
    • Added defaultErrorClassifier() function.
    • Added AutoConfig interface.
    • Added createOpenTelemetryTransport() function.
    • Added CreateOpenTelemetryTransportConfig interface.
    • Added createEmailAttributeExtractor() function.

Version 0.1.2 ​

Released on Nowember 3, 2025.

@upyo/smtp ​

  • Added STARTTLS support for secure connection upgrade. The SMTP transport now automatically detects and uses STARTTLS when connecting to servers that advertise this capability (such as Protonmail, Office 365, and others). This allows using port 587 with secure: false for automatic encryption upgrade. [#14]

Version 0.1.1 ​

Released on July 14, 2025.

@upyo/smtp ​

  • Fixed CJK character encoding corruption in SMTP transport HTML emails. Korean, Japanese, and Chinese characters are now properly encoded using UTF-8 quoted-printable encoding. [#4]

Version 0.1.0 ​

Initial release. Released on July 13, 2025.