Fix Occasional Mail Connection Errors

In your mail client, when your settings are correct you may still get an occasional connection error in some circumstances. This can often be the case when you have several devices logging into the same mail account on the same network.

Verify the Problem

The first thing to do is to make sure the error is happening at the server and not an issue with your local internet connection. Run this command to see if your connections are being maxed out:

grep 'Maximum number of connections from user+IP exceeded' /var/log/mail.log | tail

If your connections are being maxed out, you will see errors similar to this format:

Jan 13 16:01:23 myhostname dovecot: imap-login: Maximum number of connections from user+IP exceeded (mail_max_userip_connections=10): user=user@example.com, method=PLAIN, rip=8.8.8.8, lip=8.8.8.8, TLS, session=<pdrbkQm5qsRIxBae>

This indicates that your user/IP combination is hitting the maximum number of simultaneous connections to the server. This can be fixed by updating the mail_max_userip_connections value in dovecot’s configuration.

Applying the Fix

First, open the configuration file in your favorite text editor. I will be using nano in my example:

nano /etc/dovecot/conf.d/20-imap.conf

Use the search (Ctrl+w in nano) to find the value mail_max_userip_connections. Whenever you hit this limit, it is suggested to double the value in use. By default it is set to 10, so if this is the first time updating this value, set it to 20. If you still run into issues, you can increase this further.

Lastly we need to restart dovecot to apply the changes:

service dovecot restart