Postfix won't talk to spamd anymore
"spamd: bad protocol: header error: request=smtpd_access_policy"
This error, possibly showing up in /var/log/mail.info, indicates you have postfix attempting to communicate directly with spamd. Which doesn't work. "request=smtpd_access_policy" is part of the postfix protocol, which spamd does not speak. The only thing that can communicate directly with spamd is spamc.
You probably have a line in your /etc/postfix/main.cf similar to:
The significant part is the "783" - the port number of spamd.