POP3 etiquette and Submission (SMTP)

POP3 in 2026? Yes — IoT devices, scanners, ticketing systems. Dovecot's POP3 is fine; just keep these in mind:

• pop3_uidl_format = %08Xu%08Xv — required for clients that leave mail on server.
• Don't mix POP3 + IMAP on the same mailbox without pop3_no_flag_updates = yes or your "Read" flags get rewritten.

Submission (port 587 SMTP-in) — Dovecot 2.3.13+ ships its own submission service that uses the same auth as IMAP. Stops users hammering Postfix's smtpd_sasl.

protocols = imap pop3 lmtp sieve submission
service submission-login {
  inet_listener submission {
    port = 587
  }
}
submission_relay_host = 127.0.0.1
submission_relay_port = 10025

Have Postfix listen on 10025 (no auth required, just accepts from localhost).

ManageSieve (port 4190): lets users upload their own Sieve scripts via Roundcube, Thunderbird, or sieve-connect. Almost free to enable.