Microsoft is investigating an issue that prevents Outlook and other email clients from connecting when using an Outlook.com account.

"Since starting around 1/23/24 users have reported issues connecting with Outlook 2013, Outlook 2016, Outlook for Microsoft 365, Thunderbird, and mobile email apps when connecting with POP, IMAP, and Exchange connections," Microsoft says.

"Some users have reported that signing in with an App Password works to connect but later goes back into a disconnected state."

Customers reported experiencing sign-in problems linked to this issue since last Tuesday on Microsoft's community platforms and social networks like Reddit.

Those impacted see pop-up messages asking them to enter their password and giving them a "Remember my credentials" option. However, even when entering the correct password, the dialog will still pop up while the app tries connecting to the account. 

"I put in the existing app password, it tries to connect, doesn't, and the security window pops up again," one affected customer says. "I signed in online, removed the app passwords, made a new one, and tried that. Same thing. I tried my regular (non-app) password, but that didn't work as expected."

The Outlook Team is currently working on a fix for this issue and will share more information when a solution or more details are available.

Affected customers who cannot use their clients to connect to their Outlook.com accounts are advised to use Outlook.com on the web until the issue is addressed.

Other Outlook.com issues fixed in recent months

In December, the company fixed another issue, causing Outlook Desktop clients to crash when sending emails from Outlook.com accounts in Version 2311 Build 17029.20068.

Microsoft advised users who disabled auto-updates to click "Update Now" under File > Office Account > Update Options to mitigate the issue.

The Outlook team also solved a bug caused by a configuration issue that was triggering 401 exception errors and breaking email searches for Outlook.com users in July.

Earlier in June, Microsoft confirmed that some of its services, including Outlook.com, OneDrive, and the Azure Portal, were disrupted or taken down by DDoS attacks claimed by the Anonymous Sudan threat actor believed to have Russian ties.