Mario Fetka
23 lines
1.2 KiB
Markdown
23 lines
1.2 KiB
Markdown
# SMTP extensions
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Bongo keeps the classic `HELO`/`MAIL`/`RCPT`/`DATA` path for old clients and
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advertises ESMTP extensions after `EHLO`. The server advertises `8BITMIME` and
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`SMTPUTF8` only when the corresponding configuration is enabled. `SMTPUTF8`
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is accepted as a `MAIL FROM` parameter only after `EHLO`; non-ASCII envelope
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addresses require it and are validated as UTF-8.
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`BODY=8BITMIME` is recorded with the queued message and is sent to a remote
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peer only when that peer advertises `8BITMIME`. Bongo does not implement
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`BDAT`/`CHUNKING`, so `BODY=BINARYMIME` is rejected explicitly instead of
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silently treating binary data as a normal `DATA` message.
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Outgoing SMTP uses the peer's advertised `SIZE`, `8BITMIME` and `SMTPUTF8`
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capabilities. Internationalized domains are converted to their DNS
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ASCII-compatible form for MX lookup while the original UTF-8 address remains
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in the SMTP envelope. External SMTP relays use libcurl and receive the same
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`SMTPUTF8`/`BODY=8BITMIME` envelope parameters.
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Relevant standards are [RFC 6531](https://www.rfc-editor.org/rfc/rfc6531.html),
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[RFC 3030](https://www.rfc-editor.org/rfc/rfc3030.html) and
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[RFC 3461](https://www.rfc-editor.org/rfc/rfc3461.html).
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