Dovecot

Auto-Detection

Health Check

Built-in Metrics

Dovecot is a secure, open-source IMAP and POP3 email server for Unix-like operating systems.

Note

Dovecot metrics can only be produced with Dovecot version 2.3 or prior.

Auto-Detection

Bleemeo monitors the Dovecot mail server through automatic service detection by process, a service check on port 143, and built-in metrics read from the old_stats plugin on a separate port that defaults to 24242. If the auto-detected parameters are incorrect, you can override them manually — stats_port is the old_stats listener’s port, and metrics_unix_socket reads the same statistics from a unix socket instead.

Linux

sudo tee /etc/glouton/conf.d/99-dovecot.conf > /dev/null << 'EOF'
service:
  # For a Dovecot running outside a container
  - type: "dovecot"
    address: "127.0.0.1"
    port: 143   # IMAP listener; IMAPS is not supported here
    stats_port: 24242

  # For a Dovecot whose old_stats listener is a unix socket
  - type: "dovecot"
    address: "127.0.0.1"
    port: 143
    metrics_unix_socket: "/run/dovecot/old-stats"

  # For a Dovecot running in a Docker container
  - type: "dovecot"
    instance: "CONTAINER_NAME"
    port: 143
    stats_port: 24242
EOF

Windows

Dovecot does not run on Windows.

Glouton automatically detects configuration changes.

Requirements

Dovecot 2.3 or prior is required. The old_stats plugin was removed in Dovecot 2.4, and the configuration below makes a 2.4 server refuse to start.

The old_stats plugin must be enabled, with a listener Glouton can reach — an inet_listener, or the unix_listener below. Without one the service is detected and checked, but reports no metrics. In /etc/dovecot/conf.d/90-stats.conf:

mail_plugins = $mail_plugins old_stats

service old-stats {
  unix_listener old-stats {
    user = $default_internal_user
    mode = 0600
  }
  inet_listener {
    address = 0.0.0.0
    port = 24242
  }
  fifo_listener old-stats-mail {
    mode = 0666
  }
  fifo_listener old-stats-user {
    mode = 0666
  }
}

plugin {
  old_stats_refresh = 10 secs
  old_stats_track_cmds = yes
}

protocol imap {
  mail_plugins = $mail_plugins imap_old_stats
}

Restart Dovecot after the change.

The protocol imap block is what makes old_stats_track_cmds actually count commands. Without imap_old_stats, everything else still works but dovecot_num_cmds stays at zero.

The two FIFO listeners are easy to get wrong

old-stats-mail and old-stats-user must be declared as fifo_listener, not unix_listener — the latter fails outright with duplicate listener, and Dovecot does not start. Leaving them out altogether is worse: Dovecot then creates the FIFOs with mode 0600 while the mail processes writing to them run as an unprivileged user, so the server starts, logins succeed, and every counter reads zero — which looks exactly like a broken input. The give-away is in Dovecot’s own log: stats: open(/run/dovecot/old-stats-mail) failed: Permission denied.

Reading old_stats Over a Unix Socket

metrics_unix_socket points Glouton at the unix_listener instead of the inet_listener, so the statistics never have to be exposed on a TCP port. It takes precedence over stats_port, and Glouton falls back to the TCP listener when the path does not exist.

The socket is named after the listener, so the configuration above puts it at /run/dovecot/old-stats (/var/run/dovecot/old-stats on older distributions). Its mode = 0600 only lets $default_internal_user connect, and Glouton runs as the glouton user, so the listener has to let that user in:

  unix_listener old-stats {
    user = $default_internal_user
    group = glouton
    mode = 0660
  }

This is for a Dovecot installed on the machine: the path is resolved on Glouton’s own filesystem, so a Dovecot in a container is read through its inet_listener unless the socket is bind-mounted into the agent.

Service Check

Glouton opens the IMAP port and reads the server’s greeting.

Metric	Description
service_status	Status of Dovecot

Built-in Metrics

Server-wide totals, not per user or per mailbox.

Metric	Description
dovecot_num_connected_sessions	Number of Dovecot connected sessions
dovecot_num_logins	Number of Dovecot logins, per second
dovecot_num_cmds	Number of Dovecot IMAP/POP3 commands processed, per second
dovecot_auth_successes	Number of successful Dovecot authentications, per second
dovecot_auth_failures	Number of Dovecot authentication failures, per second

Monitoring Troubleshooting

See Troubleshoot a Service Check or Missing Metrics for what applies to every service: finding the address and port Glouton really uses, what each check message means, and how to read the collection error — which does not appear in the agent logs at the default level.

The Service Check is not OK

The check opens the IMAP port and expects a greeting, so beyond the usual Connection refused and connection timed out after 10 seconds it also fails when something that is not an IMAP server answers there. Pointing it at the IMAPS port (993) fails for that reason: the check speaks plain IMAP and does not negotiate TLS.

Metrics are Missing

Reproduce what Glouton does, from the machine where the agent runs:

printf 'EXPORT\tglobal\n' | nc 127.0.0.1 24242            # inet_listener
printf 'EXPORT\tglobal\n' | nc -U /run/dovecot/old-stats  # unix_listener

What you see	Cause	Fix
a connection error	The old_stats inet_listener is not configured	Add it and restart Dovecot
a connection error	The listener is on another port	Set stats_port to match
Permission denied on the socket	The unix_listener does not let the glouton user connect	Give it group = glouton and mode = 0660
metrics still read from the TCP listener	The metrics_unix_socket path does not exist, so Glouton fell back	Fix the path — it is the listener’s name under Dovecot’s base_dir
counters that all read zero	The FIFOs are missing or unreadable by the mail processes	Declare old-stats-mail and old-stats-user as fifo_listener with mode 0666
dovecot_num_cmds alone at zero	imap_old_stats is not in the imap protocol’s mail_plugins	Add the protocol imap block from Requirements
Dovecot refuses to start	The server is 2.4 or newer	old_stats no longer exists; metrics need 2.3