Facebook said Monday afternoon that a bug within the API for certain mobile devices was accidentally syncing a user's @facebook.com email address rather than their primary address.
"We are in the process of fixing this issue and it will be resolved soon," a Facebook spokesman said. "After that, those specific devices should pull the correct addresses."
Facebook said that for "most devices," the API was working correctly and pulling a user's primary email address. Certain devices, however, were "pulling the last email address added to the account rather than the primary email address." Given that Facebook recently added an update to list @facebook.com email addresses on users' Timelines, that address was pulled and synced with a user's contacts.
Facebook did not specify which devices were affected.
As a result, some people found that their emails were listed in friends' contact lists as the @facebook.com address. People fired off emails to their friends at this new address without noticing, resulting in "lost" emails that seemingly never arrived. Complex settings with Facebook Messages, however, were to blame.
Facebook said this afternoon that emails sent to @facebook.com email address from Facebook friends or friends of friends will go to your Facebook Inbox. Messages from anyone else will be sent to the "Other" folder within you Inbox. Many people - myself included - did not realise this Other inbox existed, prompting us to think our messages had disappeared into the ether.
In some cases, however, that was true. "If you've specified in privacy settings that you only want to receive messages from friends or friend of friends, then the message will bounce," Facebook said.
"We've noticed that in a very limited number of cases, the bounce email back to the original sender may not be delivered because it may get intercepted by spam filters. We are working to make sure that email senders consistently receive bounce messages."