Understanding dovecot_virtual_delivery in Dovecot

What is dovecot_virtual_delivery?

If you are facing mail delivery issues related to Dovecot's virtual user system, the problem may be with:

For the Postfix-side of the same delivery flow, see Understanding dovecot_virtual_delivery in Dovecot Mail Server (the Postfix angle). For broader mail-stack debugging, "EHLO not accepted from server!" and Fixing t_dkim_invalid (DKIM Signature Issue).

• Dovecot LDA (Local Delivery Agent) ? Handles local mail delivery to mailboxes
• Dovecot LMTP (Local Mail Transfer Protocol) ? Modern protocol for efficient virtual mail delivery
• Virtual Mailbox Configuration ? Incorrect paths or database settings
• Incorrect Permissions on Mail Directories ? Dovecot can't write to mail storage

Check Dovecot Mail Delivery Method

Dovecot delivers emails in two common ways:

1. LDA (Local Delivery Agent) > Used when Dovecot handles local mail delivery directly.
2. LMTP (Local Mail Transfer Protocol) > Used for virtual mail users and integrates better with Postfix; more efficient for high-volume mail servers.

Check which method your system uses:

sudo dovecot -n | grep -i "mail_delivery\|protocol lda\|protocol lmtp"

If using LDA, you might see:

mail_plugins = sieve
protocol lda {
    mail_plugins = $mail_plugins sieve
}

If using LMTP, you might see:

protocol lmtp {
    mail_plugins = quota sieve
}

Verify Dovecot Virtual Mailbox Configuration

If your system uses virtual mail users, make sure Dovecot is properly configured.

Check Dovecot Virtual Mail Setup

Edit the main Dovecot configuration file:

sudo nano /etc/dovecot/conf.d/10-mail.conf

Ensure the following settings are correct for a typical Maildir setup:

mail_location = maildir:/var/mail/vhosts/%d/%n

Where:

• %d > Domain name (e.g., example.com)
• %n > Username (e.g., john)

If using a MySQL/PostgreSQL backend for user authentication, also check these typically associated settings:

mail_home = /var/mail/vhosts/%d/%n
mail_location = maildir:/var/mail/vhosts/%d/%n/Maildir

Apply changes and restart Dovecot:

sudo systemctl restart dovecot

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Check LMTP Configuration

If using Dovecot LMTP (recommended), ensure it's properly configured to communicate with Postfix.

Edit the master configuration file:

sudo nano /etc/dovecot/conf.d/10-master.conf

Look for a section similar to this (location may vary by distribution):

service lmtp {
    unix_listener /var/spool/postfix/private/dovecot-lmtp {
        mode = 0600
        user = postfix
        group = postfix
    }
}

In Postfix (/etc/postfix/main.cf), ensure mail delivery is delegated to Dovecot's LMTP socket:

mailbox_transport = lmtp:unix:private/dovecot-lmtp
# or for virtual_transport if using virtual domains:
virtual_transport = lmtp:unix:private/dovecot-lmtp

Restart both services:

sudo systemctl restart postfix dovecot

Fix Mail Directory Permissions

The most common virtual delivery failure is incorrect permissions. Dovecot needs to write to the mail storage directory.

1. Ensure the dedicated vmail user exists:

id vmail

If the user doesn't exist, create it:

sudo useradd -r -d /var/mail -m -s /sbin/nologin vmail

2. Set correct ownership on your mail storage directory:

sudo chown -R vmail:vmail /var/mail/vhosts
sudo chmod -R 770 /var/mail/vhosts

3. In Dovecot configuration (/etc/dovecot/conf.d/10-mail.conf), set the user and group:

mail_uid = vmail
mail_gid = vmail

4. Restart Dovecot:

sudo systemctl restart dovecot

Check Mail Logs for Errors

If mail delivery still fails, check system logs for specific error messages.

Check Dovecot service logs:

sudo journalctl -u dovecot --no-pager | tail -n 30

Check general mail logs:

sudo tail -f /var/log/mail.log | grep -i dovecot
# On some systems:
sudo tail -f /var/log/mail.err

Common errors and their meanings:

• "Mailbox not found" > Incorrect mail_location path or missing directory.
• "Permission denied" > Wrong ownership or permissions on mail directory.
• "Connection refused" > LMTP service not running or wrong socket path.
• "User doesn't exist" > Authentication/user database misconfiguration.

Summary

By systematically checking these configuration areas, your Dovecot virtual mail delivery should work correctly!