Outlook 2016 suddenly not working

[Nanfang]

Hello,

We have several machines installed with Outlook 2016 which is connected to outlook.office365.com pop3 server. Right after July 4 holiday all these clients cannot connect to the server to download mail. The server keep complaining password is not correct but it is not the case. The client can still sending out email. I cannot figure out what is the problem but I am suspecting there is some additional requirement added on the server side and Outlook 2016 is not able to fulfill. Like authentication process or TLS encryption. I have tried to use Thunderbird to connect and there is no problem. Please offer your opinion.

Thank you so much,

Steve

[#2]

@Nanfang

Is there any reason why you use a POP3 account in Outlook 2016 with Exchange Online instead of using an Exchange account type?

Exchange Online no longer supports Basic Auth and that is what you are using when you configure via POP3. Use an Exchange account type for full feature support and connectivity via Modern Authentication (OAuth 2.0).

If you still want to continue to use POP3, you must register it as an application first within your tenant. For instructions see; Authenticate an IMAP, POP or SMTP connection using OAuth | Microsoft Learn

[#3]

Hi Robert,

Thank you for your info. We have these accounts set up with the old Godaddy email. And when Godaddy switches to Office 365 we just keep all the settings. I'm going to see what we should do. Thanks again for your comment.