Google classified ct.de as a spam thrower

In mid-June, c’t editors were surprised for the first time by an error message when attempting to send emails to external addresses from the sender domain ct.de: “Our system has detected that this message is likely suspicious due to the very low reputation of the sending domain . To best protect our users from spam, the message has been blocked.” The cause of this error message was the accepting mail server at Google, which had a low reputation for the domain ct.de. After transferring the content, they ended the SMTP session and disposed of the email immediately—the harshest penalty for an email suspected of being spam, because it won’t even be found in the recipient’s spam folder.

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On June 16, the reputation of the domain ct.de suddenly fell to its lowest value. Google did not provide an explanation.

Together with the publisher’s IT system management, we got to the bottom of the problem. The domain was not on public blacklists, Google does not use such. The first point of contact for mail admins who want to deliver to Google is the tool postmaster.google.com. There you have to log in with a Google account and activate your domain with a TXT entry in the DNS in order to be able to see statistics and error messages.

The spook began on June 19, and by the 16th the reputation had dropped to “bad”. What the platform also announced: “Missing entries in the data shown. Some data may not be available.” The hypothesis: Google had lost reputation data and the system had decided to simply devalue the domain.

There were no error messages with information about what we did wrong as the sender, and the linked documentation didn’t help either. It just says, “The better the domain’s reputation, the more likely emails will be delivered from your sending domain (SPF and DKIM) and the less likely it will end up in the recipient’s spam folder.”

The domain ct.de is not the first to fall suddenly and without explanation from Google’s favor. Again and again we receive emails from administrators of rather small mail servers who report similar things. We didn’t get any further via Google’s press office either. The European manager promised to work with a team at Google Cloud on the issue, but it ended up taking nearly a month. Emails did not start arriving again until July 17th.

This is problematic because Google servers not only supply the free accounts for Gmail. Many companies now have their emails with their own domain managed by Google. The evaluation of the Heise server for outgoing e-mails shows the role played by large providers such as Google and Microsoft. The July 28 log counted 7,168 emails to Microsoft servers over the past ten days. Google follows in third place with 4272 emails. The German providers are far behind, T-Online servers come together to 1737 mails, GMX to 1627.

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c’t 18/2023

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(jam)

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