We have a particular domain on our server which is getting SPAMMED big time by some no-life. Those SPAM emails are getting filtered like they should by Commtouch and the other filters we have in place and they always end up in the SPAM folder with like 97 SPAM-Weight.
The thing is, one of those users is forwarding all of his emails to his gmail address. I noticed that since a couple of weeks those SPAM messages always get stuck in the spool at 9/10 recipients. If I inspect the message in the spool I can see that gmail is rejecting the forward from our mailserver:
421 4.7.0 [18.104.22.168 15] Our system has detected an unusual rate of 4.7.0 unsolicited mail originating from your IP address. To protect our 4.7.0 users from spam, mail sent from your IP address has been temporarily 4.7.0 rate limited. Please visit 4.7.0 http://www.google.com/mail/help/bulk_mail.html to review our Bulk 4.7.0 Email Senders Guidelines. f19si10741414qhc.19 - gsmtp
How can we prevent this situation from happening? It would be a disaster to be blacklisted for gmail's servers. We cannot block the SPAMMER's IP or domain since they are changing them everytime and removing the forward to gmail isn't an option.
Could we setup filtering to analyse our outgoing emails or something like that? I know it's possible but i'm just not certain if it would be considered Outgoing SMTP or Incoming SMTP since this is a forward...
Anyone has a fix for this?