Thunderbird Fails to Send Emails When Setup With Office365

Tue, 21 Apr 2026 11:28:16 -0700

Now with OAuth2, you can quickly set up Thunderbird email client to use with Office 365. This comes in handy if you use the Microsoft Office Basic plan that comes without installed applications. There’s a caveat though. When you try to send an email, Thunderbird comes back with an error saying it cannot connect. There’s a lot of stuff written on the intertubes about how to solve them and much of it is outdated. The simplest solution is as follows:

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Thunderbird Fails to Send Emails When Setup With Office365