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


Nov 9, 2016
cPanel Access Level
Root Administrator

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

Last edited by a moderator:


Jurassic Moderator
Staff member
Oct 19, 2014
cPanel Access Level
Root Administrator
Hey there! This might be a better question for the spam filtering service, as it seems that something may have changed on their end, as the recipient server doesn't have a way to control the ports a connection uses. For example, if your hosting provider is blocking port 25, you won't be able to send or receive mail. While you could certainly change your mail port to another number, the incoming traffic isn't going to be aware of your custom value, so mail will still not work properly.

Could you speak with the spam filtering provider to get their thoughts on this?