Mario Fetka
67 lines
2.8 KiB
Markdown
67 lines
2.8 KiB
Markdown
# POP3 and POP3S
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Bongo keeps POP3 for simple and older mail clients while using the same
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accounts, authentication policy, message files, flags, and per-user mail quota
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as IMAP and Webmail. POP3 is an access protocol only: SMTP remains responsible
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for message submission.
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## Listeners and TLS
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The suffixless `pop3` configuration document controls the two listeners:
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```json
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{
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"version": 1,
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"port": 110,
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"port_ssl": 995,
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"allow_legacy_tls": false,
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"proxy_protocol_enabled": false,
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"proxy_protocol_networks": []
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}
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```
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Port 110 offers `STLS` before authentication. Port 995 uses implicit TLS.
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Password and GNU GSASL mechanisms are made available only on a protected
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connection under the secure default. Enabling `allow_legacy_tls` is an
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explicit compatibility exception for obsolete clients; current TLS is still
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negotiated when both peers support it.
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PROXY protocol must remain disabled unless a trusted TCP proxy is actually in
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front of POP3. Enabling it requires at least one exact trusted IPv4 address or
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CIDR in `proxy_protocol_networks`; ordinary clients must never be included.
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## Commands and capabilities
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The server implements the normal authorization and transaction commands:
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`USER`, `PASS`, `AUTH`, `APOP`, `STAT`, `LIST`, `UIDL`, `RETR`, `TOP`, `DELE`,
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`RSET`, `NOOP`, `CAPA`, `UTF8`, `STLS`, and `QUIT`. Multiline replies apply
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POP3 dot transparency and canonical CRLF termination even when a stored
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message was read in chunks.
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`CAPA` reports the implemented `TOP`, `RESP-CODES`, `AUTH-RESP-CODE`,
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`PIPELINING`, `EXPIRE NEVER`, `UIDL`, and `UTF8` features. `STLS`, `USER`, and
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the `SASL` mechanism list are state-dependent. After `UTF8` succeeds, `STLS`
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is no longer offered and is rejected, preventing already-buffered cleartext
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UTF-8 session state from crossing the TLS boundary.
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## Deletion and quota semantics
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`DELE` marks a message only for the current POP3 transaction. `RSET` or a
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disconnect leaves it in the mailbox; a successful `QUIT` commits the marked
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deletions. Storage is therefore released only after that commit. POP3 has no
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standard quota query command, but delivery to the same account is still
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limited by the shared Store quota described in [quotas.md](quotas.md).
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Use IMAP or Webmail when a client needs server-side folders, flags, searching,
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or concurrent mailbox changes. POP3 clients which delete downloaded mail
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should be tested carefully before enabling that option for a large account.
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## Operational checks
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After changing the listener or TLS policy, validate and synchronize the
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configuration, restart the agent through `bongo-manager`, and test both the
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clear listener's `STLS` transition and a direct POP3S login. Also verify
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`STAT`, `LIST`, `RETR`, `TOP`, `UIDL`, deletion rollback on disconnect, and
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deletion commit on `QUIT`. The release gate is recorded under POP-01 through
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POP-06 in [release-testing-0.7.md](release-testing-0.7.md).
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