Spamfiltering service delivering on port 465 is bounced with message about port 587 ?

Hello we receive mail from a mail-filtering service that relays back mail via port 465. Our MX point to this mail-filtering service. Since today the delivery on port 465 is triggering a bounce with message : SMTP error from remote mail server after RCPT TO:<******************>: 550 SMTP AUTH is required for message submission on port 587. The message speaks about port 587, the logs of the spamfiltering service talks about port 465 ! PS : All domains of the filtering-service are in /etc/backupmxhosts All IPs of the filtering-service are in /etc/senderverifybypasshosts and /etc/trustedmailhosts The source-IP that is bounced *is* in the list of senderverifybypasshosts and trustedmailhosts Thanks