This is a python script and targeted postfix configuration designed to create postfix log data that is close to real world mail load. It has only been tested on CentOS 7 but should be very portable across distros.
One difference is that the extended delivery status info usually seen after 'status=' is not there, as messages are discareded to avoid actually delivery attempts from being made.
From and to addresses are randomly generated before the @domain.com part of the address to allow unique to/from parsing of logs via queries if needed.
#Log Example: Apr 1 15:32:46 localhost postfix/discard[23132]: 9FA7140BE989: to=HDYAVORGEDQZ@source.com, relay=none, delay=0.02, delays=0.02/0/0/0, dsn=2.0.0, status=sent (source.com)
Apr 1 15:32:51 localhost postfix/error[23106]: 5D02540BE988: to=MVVMZFTSJUBG@deferred.com, relay=none, delay=0.02, delays=0.01/0/0/0.01, dsn=4.3.0, status=deferred (mail transport unavailable)
Apr 1 15:32:56 localhost postfix/error[23054]: 88B2D40BE989: to=NVJUEPFETBBU@bounced.com, relay=none, delay=0.04, delays=0.03/0/0/0, dsn=5.0.0, status=bounced (mail for bounced.com is not deliverable)
Apr 1 15:32:56 localhost postfix/discard[23132]: 8FA2940BE98C: to=OTVHVBYSSFBS@source.com, relay=none, delay=0.02, delays=0.02/0/0/0, dsn=2.0.0, status=sent (source.com)
Apr 1 15:33:01 localhost postfix/discard[23132]: 5DFC040BE989: to=UYSLCXUJNXED@sent.com, relay=none, delay=0.01, delays=0.01/0/0/0, dsn=2.0.0, status=sent (sent.com)
Apr 1 15:33:06 localhost postfix/error[23106]: 5D36740BE989: to=RSZNUCTBVDPD@deferred.com, relay=none, delay=0.05, delays=0.04/0/0/0.01, dsn=4.3.0, status=deferred (mail transport unavailable)
#Quick Start copy the main.cf and transport_maps file into /etc/postfix
execute the 'postmap transport_maps' command
execute the 'postfix reload' command
postfix should now be configured to properly handle the domains used by the script
place the script in the location you will run it from. Currently I run this from /root/bin but you can run de-elevated if you like.
Call script into the background via 'nohup ./postfix_loadgen.py &'
watch the /var/log/maillog files to ensure there are no issues.