The bug was spotted late last month over on josh.com. Microsoft quickly confirmed the issue, creating an official support page to help users recover from the potentially devastating effects. It has now released a patch that cures the problem, albeit only to Office Insiders for now.
The issue only affects older POP3 email accounts. People using Outlook with a modern service, such as Gmail or Microsoft’s own Outlook.com, shouldn’t be impacted as POP3 has now been largely replaced by IMAP. The older protocol remains in use by many other services though, including corporate environments.
The bug lies in Outlook’s “Leave a copy of messages on the server” setting. The program does anything but this with the feature enabled though, doing the exact opposite and deleting everything. With the checkbox option unticked, Outlook instead creates copies of messages on the server, leading to duplicate emails being downloaded.
“After Outlook downloads your email, all the email messages on the server are deleted from the Inbox,” Microsoft wrote in its support article. “Email messages are downloaded multiple times in Outlook, causing duplicate items. This issue may occur if you have Outlook 2016 version 16.0.6568.2025 configured to use POP3, and if you have the Leave a copy of messages on the Server option enabled.”
Tests performed by josh.com confirmed both bugs. Microsoft has since responded, advising users switch to using IMAP for email where possible. Since the only real reason to continue using POP3 today is for compatibility reasons, this won’t be an option for many people though.
Microsoft’s alternative fix is to rollback to Outlook 2013 or 2010, another solution that won’t really be feasible for the majority of users. The company has since followed up with an Office update that should be more useful.
A new preview version of Office 2016 was issued to Office Insiders yesterday that finally provides a proper fix for the issue. Assuming it makes it through public testing with the Insiders, Microsoft will likely rush this update out to general users as soon as possible. The company admits the latest version of Outlook 2016 has “significant POP3 issues” that may leave users experiencing duplicate emails and unexpected deletions.
The bug could prove costly for some users. Consumers who install new Office updates automatically as recommended and still use POP3 email accounts may be left with some of their mail permanently deleted. Unless a backup of the messages or mail server is available, much of the chaos caused by Outlook will be irreversible.
