Knownhost, Cpanel, WHM causing email forwarders to be blocked!
On Thursday, I noticed that, after 3 hours, I was suddenly getting next to no emails on my work email address, which is extremely unusual, if I go five minutes without an email coming, that’s unusual. I work in rental home marketing, so I have forwarding email addresses for new leads, which forwards to me, for marketing effectiveness reasons, and the property manager, to follow up on the lead.
At the same time, I also saw a bunch of messages bouncing with a response saying; “Remote Server returned ‘550 5.7.520 Access denied, Your organization does not allow external forwarding. Please contact your administrator for further assistance. AS(7555)‘” on my Office 365 based email, so I started thinking that Google, who provides our email, was blocking auto-forwarded emails. I have my Microsoft-based email forwarding to my Google-based email, so I wouldn’t have to check two email accounts.
I later found that the above error message is a result of a change to the security settings in Office 365 and nothing to do with my issue. Nonetheless, this sent me down the wrong troubleshooting path.
I logged into my Cpanel and checked Email -> Track Delivery logs and found that all my forwarded email was being blocked and discarded by RBL (remote block list), Spamhaus. After doing some research I found how to disable the RBL checking, by logging in to WHM and going to Exim Configuration Manager -> RBLs tab, where you can disable spamcop.net and spamhaus.org RBLs.
This solved half of my issues, I was still having issues with not receiving some email, notably Craigslist post confirmations. So back into Cpanel I went and clicked about in the Email section until I clicked on Configure Greylisting, where I found that all our domains were set to enable Greylisting, I disable this anti-spam feature on all domains and everything returned to, in fact, better than normal.
Knownhost is our VPS provider, I’m not sure if they were the cause of these issues with their VPS configurations, or whether this is the way WHM/CPanel comes. I think it might be the former, as I noticed in WHM -> Exim Configuration Manager -> RBLs that the default setting was off for RBL: bl.spamcop.net and RBL: zen.spamhaus.org, but both were enabled, and I was not the person who changed it to on.
I’m not trying to apportion blame, I wrote this article in the hope that it might help others with the same issue. But it does have me wondering how many emails were discarded over the past seven years? were these options already turned on when I purchased the VPS plan or was it enabled on Thursday morning when I noticed that there was an issue, suffice to say, I really hope it was the latter option.