Dovecot Basics

Page 13 — IMAP/POP3 server. Mailbox access and authentication.

What Dovecot is

Dovecot handles:

• IMAP and POP3 access — letting users read their mail from clients
• Mailbox storage and management
• Authentication for mail access (and sometimes as an auth backend for Postfix via SASL)

Postfix moves mail between servers. Dovecot lets users access their mailboxes. They work alongside each other — Postfix delivers incoming mail into the mailbox; Dovecot serves it to clients.

Listener ports

# Default listener ports:
143   IMAP (STARTTLS upgrades from plaintext)
993   IMAPS (TLS from the start — older but still widely used)
110   POP3 (STARTTLS)
995   POP3S (TLS from the start)

# Check which ports Dovecot is actually listening on
ss -tlnp | grep dovecot
lsof -i -P -n | grep dovecot

LMTP — receiving mail from Postfix

In a typical setup, Postfix delivers locally-addressed mail to Dovecot via LMTP rather than writing mailbox files directly. This lets Dovecot handle delivery, indexing, and sieve filters.

# In Postfix main.cf — deliver via Dovecot LMTP socket
virtual_transport = lmtp:unix:private/dovecot-lmtp
# or over TCP:
virtual_transport = lmtp:inet:localhost:24

# In Dovecot /etc/dovecot/conf.d/20-lmtp.conf:
protocols = imap pop3 lmtp
# The LMTP socket is created by Dovecot at: /var/spool/postfix/private/dovecot-lmtp

TLS check

# Verify Dovecot TLS certificate and connection
openssl s_client -connect mail.example.com:993 -quiet
# Look for: subject, issuer, verify return code = 0 (ok)

# Test IMAP over STARTTLS (port 143)
openssl s_client -connect mail.example.com:143 -starttls imap

Common files

/etc/dovecot/dovecot.conf
/etc/dovecot/conf.d/

Main config is dovecot.conf. The conf.d/ directory contains split configuration files loaded in order. Key files:

• 10-auth.conf — authentication settings
• 10-mail.conf — mailbox location
• 10-ssl.conf — TLS settings
• 20-imap.conf, 20-pop3.conf — protocol settings

Useful commands

doveconf

doveconf
doveconf -n

Shows the effective Dovecot configuration. -n shows non-default values only — like postconf -n for Postfix.

doveadm who

doveadm who

Shows currently connected users and sessions.

doveadm user

doveadm user '*'

Shows mailbox and user info for all users (depending on auth backend setup).

Service checks

systemctl status dovecot
journalctl -u dovecot -n 50

Troubleshooting

• Service status and recent logs
• Config check: doveconf — look for errors
• Login failures in logs — check for bad password or unknown user
• Mailbox location permissions — can Dovecot read the mailbox directory?
• Auth backend issues (PAM, LDAP, SQL, FreeIPA/SSSD)
• TLS cert valid and permissions correct on key file