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>
ZacharyZhang-NYandClaude Opus 5.5
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