When working with Dovecot IMAP servers, you might encounter the permission error:

dovecot: imap(ec2-user): Error: user *theuser*: Couldn't drop privileges: Mail access for users with UID 222 not permitted

This typically occurs when Dovecot's security restrictions prevent a user session from starting due to UID-based access control.

The error stems from Dovecot's default configuration which restricts mail access to specific UID ranges. The main culprits are:

• first_valid_uid setting in dovecot.conf
• System user UID falling outside permitted range
• Incorrect permission inheritance

Here's how to modify your Dovecot configuration to resolve this:

# /etc/dovecot/conf.d/10-master.conf
service imap {
  # Ensure the minimum UID is low enough
  first_valid_uid = 100
}

# Alternative global setting in 10-mail.conf
mail_uid = 222
mail_gid = 222
first_valid_uid = 100
last_valid_uid = 5000

After making changes, verify with:

dovecot -n  # Check current configuration
systemctl restart dovecot
tail -f /var/log/mail.log  # Monitor for errors

For more complex environments, consider:

# Check user's actual UID:
id -u username

# For systemd systems, check service constraints:
systemctl show dovecot | grep Protect
systemctl edit dovecot  # Add overrides if needed

When lowering UID restrictions:

• Audit all users in the expanded UID range
• Consider using mail_access_groups instead of UID ranges
• Implement additional PAM restrictions if needed

When you encounter the error message Couldn't drop privileges: Mail access for users with UID 222 not permitted in Dovecot, it's typically related to security restrictions in your configuration. Dovecot refuses to start the IMAP service because it's attempting to drop privileges to a UID that isn't explicitly permitted.

This error occurs because of these common scenarios:

• The UID (222 in this case) isn't listed in Dovecot's first_valid_uid/last_valid_uid range
• The system user doesn't have proper mail directory permissions
• Dovecot is configured with too restrictive UID/GID settings

Check your /etc/dovecot/conf.d/10-mail.conf file for these settings:

# Example of proper UID range configuration
first_valid_uid = 100
last_valid_uid = 2000

# Or to specifically allow UID 222
mail_uid = 222
mail_gid = 222

First, confirm the UID of your mail user:

id -u theuser

Then verify the mail directory permissions:

ls -ld /var/mail/theuser

Here's a tested configuration that resolves this issue:

# /etc/dovecot/conf.d/10-mail.conf
mail_location = maildir:~/Maildir
mail_privileged_group = mail
first_valid_uid = 100
last_valid_uid = 65000

# /etc/dovecot/conf.d/10-auth.conf
auth_mechanisms = plain login
!include auth-system.conf.ext

Enable verbose logging to get more details about the authentication process:

# /etc/dovecot/conf.d/10-logging.conf
auth_verbose = yes
auth_debug = yes
mail_debug = yes

After making changes, always test your configuration:

dovecot -n
systemctl restart dovecot

If you're using systemd, you might need to adjust service restrictions:

# /etc/systemd/system/dovecot.service.d/override.conf
[Service]
ReadWritePaths=/var/mail
PrivateTmp=false

For SELinux systems, don't forget to check security contexts:

restorecon -Rv /var/mail