Found in /var/log/syslog

Apr 28 10:43:07 atlantis amavis[1414]: (01414-07) NOTICE: reconnecting in response to: err=2006, HY000, DBD::mysql::st execute failed: MySQL server has gone away at (eval 114) line 166, <GEN156> line 5

This is not an error. Amavis is run as a daemon and sometimes MySQL server closes the connection that Amavis had opened if it is not used in a while.

If you do not like getting this error by OSSEC edit /var/ossec/rules/local_rules.xml and add this blok inside <group name="local,syslog"> ... </group> block:

 <rule id="100050" level="2">
   <if_sid>1002</if_sid>
   <match>NOTICE: reconnecting in response to: err=2006, HY000, DBD::mysql::st execute failed: MySQL server has gone away at (eval 97) line 166</match>
   <description>Ignore Amavis complaining about MySQL going away</description>
 </rule>