Thanks for the suggestion, I found them in the log:
/var/log/maillog.processed:Jan 25 20:10:37 vps postfix/qmgr[5251]: 6B79F118A534: from=<
[email protected]>, size=4377, nrcpt=1 (queue active)
/var/log/maillog.processed:Jan 25 20:10:37 vps postfix-local[9624]: postfix-local...