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April 7th, 2008

Gmail Being Blocked By Some Anti-Spam Vendors

Thousands of users are experiencing problems receiving e-mail from Gmail users recently. Over the past month, major anti-spam vendors have had to apply scrutiny to Gmail in a way they haven’t had to before, and the result is reduced delivery performance and sometimes outright blocking of Gmail. Some messaging hosts are being instructed to reject SMTP connections from Google.

The reason is defeated CAPTCHA for Gmail that was announced in February. According to sources around the anti-spam industry, the result has been a marked increase in spam originating from Gmail SMTP servers. Some say the spam increase started even earlier.

A support analyst with MessageLabs, a major provider of software-as-a-service anti-spam filtering, said that “some spammers have hacked into the Gmail captcha system, and were able to relay spams appearing to come from Googlemail’s IP addresses. This has caused many IPs of theirs to appear to be sources of spam.” For their customers, this means a decrease in performance. “We have a traffic-shaping system that throttles IPs that we believe to appear to be a source of spam. The result is that for the past couple of days we have been seeing issues like this with Gmail,” the analyst concluded.

Gmail has sent out a lot of spam recently, and they are registering on traffic shaping systems. When spam is sent out over a Gmail relay, that relay can sometimes get completely blocked, causing problems for thousands of legitimate Gmail users. MessageLabs then has to throttle only the SMTP relays that are spamming.

Blocking problems has been verified, as well as extremely long delays in delivering messages. Delays of four hours and up to 24 hours have been seen. The problem can be maddening because not all Gmail relays are affected. Hence you may be getting some e-mail on time, while others aren’t coming through. Even some corporate Google e-mail has been blocked.

Postini (which was acquired by Google last year) anti-spam filtering service does not appear to be affected at this time. Purely client-side filters such as SpamBayes are also not affected.

The damage currently appears limited to select SaaS filtering solutions, such as MessageLabs and Antigen. There are unconfirmed reports from Microsoft as well. A source at another anti-spam company who wished to remain anonymous did say that Google can expect more problems if the CAPTCHA crack cannot be stopped. His product team was already working on the issue, but they were unsure how best to handle it.

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