This error might pop up as you are trying to setup your email server. Fear not, there is a good chance that this is not a major issue and can be solved by running one single line of code in the command line.
yum install dovecot-mysql
Yep thats it. Dovecot has a mysql driver that it requires in order to be able to communicate with an SQL database. Once you have it installed you should be able to gain access to the database.
service dovecot restart
Make sure to restart dovecot so the changes take effect.