This happened on a recent cPanel server. Dovecot was showing this error message while restarting the service:
Starting Dovecot Imap: Warning: fd limit (ulimit -n) is lower than required under max. load
The fix was quick and easy. You just need to reconfigure dovecot and rise the file descriptor limits.
Edit dovecot configuration file:
nano -w /etc/sysconfig/dovecot
Add this at the end:
ulimit -n 4096
Output example on how it should look after edit:
[email@example.com:~]cat /etc/sysconfig/dovecot # Here you can specify your dovecot command line options. # #OPTIONS="" ulimit -n 4096
Restart dovecot and exim once again:
service dovecot restart
service exim restart
That should get rid of that warning message.