Update: Matt Cutts has chipped in around the web saying that this isn’t true — including in the comments below. Read Matt Cutts: Your newsletter won’t affect your search rankings after all for more information.

Even if your site’s content is up to scratch, Google will penalize your website if you’ve got too many inactive users subscribed to a newsletter with a reply address from the same domain name, LockerGnome’s Jake Ludington reports after investigating his own site’s drop in search traffic.

Google is now using the information it gleans from its Gmail users to improve its spam filtering functionality to penalize accompanying sites in its search listings. Even if you follow best practices for email marketing, Ludington’s report says, you’re still likely to be in trouble. If you have a high number of legitimate subscribers who don’t open your emails regularly, your site is likely to end up in the search engine’s spam bin.

The good news is that the problem can be fixed. Most providers of email marketing services, such as Aweber and Mailchimp, provide you with detailed information on which subscribers are opening your emails regularly and which are letting them gather dust or just deleting them without reading them.

Ludington suggests that removing these users manually is more effective than asking your users to repeat their opt-in — those who lost interest are likely to lose interest again.

“I chose a cutoff date. Anyone who subscribed before that date and hadn’t engaged with the newsletter in the last 90 days was deleted from my subscriber database. I started with @gmail.com addresses, because those were the ones closest to my source of pain. I then expanded my purge to anyone who matched my criteria from any domain. I purged about 13,000 subscribers. I’m now repeating this process at the end of every month,” says Ludington.

Once you’ve completed a purge of your mailing list’s cruft, you can use Google’s reinclusion request form to get back into the index. Ludington’s story ends happily: after he described in detail what he had done and how he plans to prevent the issue from appearing again, Google removed his site from the spam bin.