There is a technology used by some ISPs to protect them against spam. The name of the service is Proofpoint, and the name of the company is Cloudmark. Recently, they adjusted what they call "our reputation" due to spam coming from our IP.
It's astounding to me that this can happen in 2023. There are three technologies now available to confirm that mail is coming from a legitimate domain;
SPF (Sender Policy Framework authentication) and
DMARC (Domain-based Message Authentication Reporting & Conformance) and
DKIM (DomainKeys Identified Mail). Cloudmark uses none of them. They base their service on the reputation of an IP address. (Which is particularly ironic when you look at the domain that I chose for the explanation of DKIM.)
The problem is, IP addresses nowadays are not permanent. They change regularly. Any service that blocks spam based on IP address is basically using a sledgehammer to smack a flea. I stopped using IP blocks on Stovebolt several years ago because they were so unreliable.
Our domain has NEVER sent spam. There are only two people authorized to send email through our server from a foreign domain; me and the Millimans. Our server only accepts encrypted connections, and it WILL NOT accept outgoing mail from anyone unless they login through that encrypted connection. Furthermore, we have had SPF, DKIM, and DMARC configured for years, as can be confirmed by querying our domain. Any competently-configured mail server does these checks routinely on EVERY SINGLE EMAIL that it receives before delivering it to the final recipient.
I have given Cloudmark a piece of my mind regarding their dumb-as-a-post service, and they have assured me that they have "adjusted our IP address's reputation". But that is meaningless. This WILL happen again. I can guarantee it.
Currently, mail from/to both centurylink and comcast is affected. You might want to notify the support folks at your ISP (if it's one or the other of these two) that they should stop using Proofpoint because it's clearly the most antiquated and ignorant technology available.
When your email to stovebolt is being rejected, you should receive a notice to that effect. It will look like this:
The part highlighted in red explains why the mail was rejected. If you see something like this, please notify me immediately. Since you can't send me email at stovebolt, you will have to send it to my home address:
paul.schmehl@gmail.com
