==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): 0.9.9
- Deployed with iRedMail Easy or the downloadable installer? iRedAdmin-Pro-MYSQL
- Linux/BSD distribution name and version: Ubunutu 16.04LTS
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MARIADB MYSQL
- Web server (Apache or Nginx):Apache
- Manage mail accounts with iRedAdmin-Pro? Yes
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.

It looks like this on the dovecot log when some one tries to log in:
Dec 30 19:20:24 pop3-login: Info: Internal login failure (pid=24453 id=1) (internal failure, 1 successful auths): user=<vidal@diamondsb.com>, method=PLAIN, rip=10.10.1.196, lip=10.10.0.8, mpid=24455, TLS, session=<fq2iN0d+bvkKCgHE>
====
This happened after a full upgrade from 9.5 to 9.9 and updated the iredAdminPro from 2.5 to 3.0
Cannot log into mail boxes says failure to auth despite using correct password all users have this issue

oot@mail:/var/log/mysql# tail -f error.log
2018-12-30T22:28:12.323050Z 8094 [Note] Access denied for user 'netdata'@'localhost' (using password: NO)
2018-12-30T22:28:12.323769Z 8095 [Note] Access denied for user 'netdata'@'localhost' (using password: NO)
2018-12-30T22:28:12.324297Z 8096 [Note] Access denied for user 'netdata'@'localhost' (using password: NO)
2018-12-30T22:28:12.326100Z 8097 [Note] Access denied for user 'netdata'@'localhost' (using password: NO)
2018-12-30T22:28:12.327312Z 8098 [Note] Access denied for user 'netdata'@'localhost' (using password: NO)
2018-12-30T22:28:12.358770Z 8099 [Note] Access denied for user 'stats'@'localhost' (using password: YES)
2018-12-30T22:28:12.360670Z 8100 [Note] Access denied for user 'admin'@'localhost' (using password: YES)
2018-12-31T00:03:04.472405Z 8392 [Note] Aborted connection 8392 to db: 'vmail' user: 'vmail' host: 'localhost' (Got an error reading communication packets)
2018-12-31T00:03:04.472423Z 8394 [Note] Aborted connection 8394 to db: 'iredapd' user: 'iredapd' host: 'localhost' (Got an error reading communication packets)
2018-12-31T00:03:04.472434Z 8393 [Note] Aborted connection 8393 to db: 'amavisd' user: 'amavisd' host: 'localhost' (Got an error reading communication packets)

Can't log into web mail but seems to be some kind of Auth issue here is dovecot log