====== Fix (un)common errors in /var/log/mail.log ======

===== postfix =====

  warning: database /etc/aliases.db is older than source file /etc/aliases
run
  newaliases

===== spamassassin =====

  WARN: bayes: database version  is different than we understand (3), aborting!’ in logs.
use mysql query
  insert into spamassassin.bayes_global_vars (variable, value) VALUES ("VERSION", 3);Jan 18 08:40:17 server amavis[25863]: (25863-01) (!!)ClamAV-clamd 

* * *

  info: config: failed to parse line, skipping, in "/etc/spamassassin/local.cf": use_dcc 0

add
  loadplugin Mail::SpamAssassin::Plugin::DCC
to ''to /etc/spamassassin/local.cf'' before //use_dcc//
===== clamav =====

  av-scanner FAILED: run_av error: Too many retries to talk to /var/run/clamav/clamd.ctl 
  (Can't connect to UNIX socket /var/run/clamav/clamd.ctl: Connection refused) at (eval 89) line 309.

//clamav// package is not enough. If you need clamd, you may also want to run
  apt-get install clamav-daemon
  
* * *
  ClamAV-clamd av-scanner FAILED: CODE(0x10fc620) unexpected ,  lstat() failed: Permission denied. ERROR\n" at (eval 111) line 899.

Add //clamav// user to the //amavis// group.
  sudo usermod -a -G amavis clamav
and then restart the clamav and amavis daemons.
  service clamav-daemon restart
  service amavis restart