Dovecot is an IMAP, POP3, ManageSieve, and LMTP server written in C by Timo Sirainen. It is not an MTA — it doesn't relay mail between servers. It receives mail from an MTA (usually Postfix), stores it, and serves it to clients.
Where Dovecot fits in the stack:
Internet → MTA (Postfix) → LMTP → Dovecot → Maildir/mdbox on disk
↑
IMAP/POP3 ← Dovecot ← clients (Outlook, iOS, Thunderbird)
What Dovecot provides:
| Service | Default port |
|---|---|
| IMAP | 143 (STARTTLS) |
| IMAPS | 993 (implicit TLS) |
| POP3 | 110 |
| POP3S | 995 |
| ManageSieve | 4190 |
| LMTP | 24 (or unix socket) |
| Submission | 587 (newer versions) |
Why Dovecot dominates:
- Fastest IMAP server with proper indexing (mdbox > 100k msgs/folder no problem).
- Modular auth: PAM, passwd-file, MySQL, PostgreSQL, LDAP, OAuth2.
- Strong replication, proxying, and director clustering.
- Sieve scripting for server-side filtering.
- Sane defaults — most production sites tweak <20 settings.
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