To find out which message is which and find connections between postfix maillog information and wallace pykolab.log information, wallace could respond with information about the file name in wallace queue. For that wallace/__init__.py file, method process_message, somewhere around line 333, could have:

return "250 OK Message %s queued" % filename

instead of just

return

That would generate such lines in maillog file:

Apr 13 17:01:40 prdlnx81 postfix/smtp[18670]: 1765140CD0: to=<recipient@domain>, relay=127.0.0.1[127.0.0.1]:10026, delay=0.02, delays=0.02/0/0.01/0, dsn=2.0.0, status=sent (250 OK Message /var/spool/pykolab/wallace/tmpdPXDIU queued)

Now it is clear what to look for in /var/log/kolab/pykolab.log file