The reader walks the MIME tree with its container context: alternative
picks versions, related finds its root by start, attached multiparts
stay whole, digest children are messages. Nesting deeper than 64
levels, counting enclosed messages, is refused, and over-deep parse
results are taken apart iteratively so dropping them cannot overflow
the stack. Composite parts with a Content-ID are cid targets.
The writer keeps attachment parameters and Content-IDs, writes
multipart and message attachments unencoded, and makes its own
Message-ID. SMTP adds BODY=8BITMIME for 8-bit bodies and SMTPUTF8
when any header block at any depth is 8-bit.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
TLS or STARTTLS with the system trust store; password and XOAUTH2
logins keep the server's words on refusal. IMAP and POP3 are written
in the engine (imap-proto parses IMAP replies): async-imap dropped
NO/BAD on LIST and FETCH and lost BYE text, async-pop kept dot
stuffing and logged passwords. SMTP runs its own transaction with
RFC 5321 mailbox checks, full dot transparency, SMTPUTF8 and RSET.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
ZacharyZhang-NYandClaude Opus 5.5