Add the following $ActionFileDefaultTemplate RSYSLOG_TraditionalFileFormat to /etc/rsyslogd.conf to have a traditional file format like this:
Jan 12 15:51:07 sles29 dovecot: imap-login: Aborted login (no auth attempts in 0 secs): user=<>, rip=172.16.12.151, lip=172.16.60.15, session=
Jan 12 15:51:14 sles29 postfix/smtpd[9226]: connect from unknown[172.16.12.151]
Jan 12 15:51:14 sles29 postfix/smtpd[9226]: disconnect from unknown[172.16.12.151]
Jan 12 15:51:17 sles29 postfix/postfix-script[10446]: stopping the Postfix mail system
Jan 12 15:51:17 sles29 postfix/master[9120]: terminating on signal 15
instead of this:
2016-01-12T15:50:14.273797+00:00 sles29 postfix/smtpd[9226]: connect from unknown[172.16.12.151]
2016-01-12T15:50:14.274207+00:00 sles29 postfix/anvil[9231]: statistics: max connection rate 1/60s for (smtp:172.16.12.151) at Jan 12 15:40:14
2016-01-12T15:50:14.274534+00:00 sles29 postfix/anvil[9231]: statistics: max connection count 1 for (smtp:172.16.12.151) at Jan 12 15:40:14
2016-01-12T15:50:14.274781+00:00 sles29 postfix/anvil[9231]: statistics: max cache size 2 at Jan 12 15:41:53
2016-01-12T15:50:14.281123+00:00 sles29 postfix/smtpd[9226]: disconnect from unknown[172.16.12.151]