==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): 1.1
- Deployed with iRedMail Easy or the downloadable installer? downloaded
- Linux/BSD distribution name and version:  ubuntu 18.04
- Store mail accounts in which backend (LDAP/MySQL/PGSQL):  MySQL
- Web server (Apache or Nginx): Nginx
- Manage mail accounts with iRedAdmin-Pro? no
====

In dovecot log, I'm getting constantly this errors:

Feb 10 10:07:14 mail dovecot: lda: Fatal: Internal error occurred. Refer to server log for more information.
Feb 10 10:07:14 mail dovecot: master: Dovecot v2.2.33.2 (d6601f4ec) starting up for pop3, imap, sieve, lmtp (core dumps disabled)
Feb 10 10:07:14 mail dovecot: auth-worker(20321): Warning: mysql: Query failed, retrying: Lost connection to MySQL server during query (idled for 0 secs)
Feb 10 10:07:14 mail dovecot: auth-worker(20321): Error: mysql(127.0.0.1): Connect failed to database (vmail): Can't connect to MySQL server on '127.0.0.1' (111) - waiting for 1 seconds before retry
Feb 10 10:07:14 mail dovecot: dict(20333): Error: mysql(127.0.0.1): Connect failed to database (vmail): Can't connect to MySQL server on '127.0.0.1' (111) - waiting for 1 seconds before retry
Feb 10 10:07:14 mail dovecot: dict(20333): Error: mysql(127.0.0.1): Connect failed to database (vmail): Can't connect to MySQL server on '127.0.0.1' (111) - waiting for 1 seconds before retry
Feb 10 10:07:15 mail dovecot: auth-worker(20321): Error: mysql(127.0.0.1): Connect failed to database (vmail): Can't connect to MySQL server on '127.0.0.1' (111) - waiting for 5 seconds before retry
Feb 10 10:07:15 mail dovecot: dict(20333): Error: mysql(127.0.0.1): Connect failed to database (vmail): Can't connect to MySQL server on '127.0.0.1' (111) - waiting for 5 seconds before retry
Feb 10 10:07:15 mail dovecot: dict(20333): Error: mysql(127.0.0.1): Connect failed to database (vmail): Can't connect to MySQL server on '127.0.0.1' (111) - waiting for 5 seconds before retry
Feb 10 10:07:21 mail dovecot: dict(20333): Error: sql dict: commit failed: Deadlock found when trying to get lock; try restarting transaction