Postfix server: Mailman email double checked with SpamAssassin

I have set up postfix with spamassassin, and then added mailman for mailing list management, everything on Debian 9 Stretch: postfix: 3.1.8 mailman: 2.1.13 spamassassin: 3.4.1 The problem is that the mail that is reinjected by MailMan is re-checked by SpamAssassin for each single recipient of mailing lists, which puts quite some burden on the system. Since the mail is already checked when originally accepted, I would like to circumvent the second spam check. The configuration is as follows: Mailman has MTA='Postfix' in the mm_cfg.py file. Postfix ======== main.cf ------- virtual_alias_maps = hash:/etc/postfix/virtual, hash:/var/lib/mailman/data/virtual-mailman master.cf ---------- smtp inet n - y - - smtpd .... -o content_filter=spamassassin smtps inet n - y - - smtpd .... -o content_filter=spamassassin submission inet n - y - - smtpd ... -o content_filter=spamassassin -o receive_override_options=no_milters ... spamassassin unix - n n - - pipe user=debian-spamd argv=/usr/bin/spamc -f -e /usr/sbin/sendmail -oi -f ${sender} ${recipient} What would be a possible way to make SpamAssassin skip the check on email delivered from MailMan?