The splash damage from Facebook's forced addition of @facebook.com e-mail addresses to users' profiles has carried over to phone contacts. Users who have given Facebook permission to sync information from the site to their phone's contacts have noticed that since the great e-mail address donation, legitimate e-mail address entries have been replaced with Facebook ones (as reported by CNET). As a result, some messages have been going to unintended locations or have become hidden. And there's no easy way to revert the changes.

Facebook started allowing users to create e-mail addresses that would direct e-mails to Facebook inboxes in November of 2010. Apparently, not enough users voluntarily bought into the feature. Around June 23, Facebook gave all users an @facebook.com e-mail with their User ID as the handle. The site also forced these to become the default display e-mail, displacing addresses that had already been set by the user. While it's easy enough to switch the display e-mail back to an actual e-mail address, Facebook didn't notify users in any way that the change was happening. Hence, it can easily go unnoticed.

The change's consequences have now carried over to any users who allow Facebook to sync contact info from their friends' accounts. For many users, friends' real e-mail addresses have been replaced with @facebook.com ones. As a result, users have been sending e-mails to their friends' Facebook inboxes, making it easy to lose track of the message and any replies following (especially if those users have alerts turned off). Worse, if the e-mail isn't coming from an address that Facebook knows about, the message will be filtered into the "Other" inbox. There, users receive no alerts that it exists at all.

Even if users turn off the information sync setting on Facebook, the e-mail address changes won't revert. So address books will be permanently broken, overrun with @facebook.com addresses. The damage can only be undone if all contacts switch their display e-mail back to a non-@facebook.com address, or if the user de-syncs from Facebook... then goes back to change all the addresses by hand.

Update: The Verge reports that Facebook says the contact sync is a bug that it intends to fix. According to Facebook, when the API is working correctly, it pushes the primary e-mail address to contacts; for some devices, the API is pushing the last e-mail address added to the account. Even if Facebook fixes the API to only push the primary e-mail, it seems to us the problem will persist, since Facebook forced many users' display e-mails to their @facebook.com address. The API bug fix will only remove @facebook.com e-mails once users manually change their display e-mails back (we've already explained how to do that).