First, make sure that your server setup matches this: - incoming: outlook.office365.com, port 993, SSL/TLS, Oauth2 (assuming IMAP) - outgoing: smtp.office365.com, port 587, STARTTLS, Oauth2

First, make sure that your server setup matches this: - incoming: outlook.office365.com, port 993, SSL/TLS, Oauth2 (assuming IMAP) - outgoing: smtp.office365.com, port 587, STARTTLS, Oauth2

I'm in POP3, for incoming messages the default port is 995 (anyway, incoming messages work) The other specs are exactly what you wrote.

Are you using your full email address, including the text to the right of the @?

yes, I do

Please post the complete error messages that you receive.

Hello, Messages are in french : First one https://assets-prod.sumo.prod.webservices.mozgcp.net/media/uploads/images/2024-12-09-08-55-08-dd6f2c.png Approximative translation : "failure of the connection from the smtp.office365.com server with the user name xxxx@outlook.com" "Try Again" "Enter a new password" "Cancel" If I click "Try Again" or "Enter a new password", thunderbird tries again and come back on the same message (It's weird but if I want to enter a new password, I can't do it from this screen. But I checked the password many times)

If I click "Cancel" I get a second message : https://assets-prod.sumo.prod.webservices.mozgcp.net/media/uploads/images/2024-12-09-09-02-19-63d0cd.png "Sending the message has failed" "Impossible to authenticate on the outgoing server (SMTP). Please check your password an the <<Authentication method>> in the menu <<Accounts parameters | Outgoing server (SMTP)>>"

Hope it helps Michel

I forgot to translate the "titles" of the windows : 1) "Failure of the connection to the account <<Outlook.com (Microsoft)>> 2) "Error sending message"

Ok, I would like someone with more experience with Outlook to see this thread, as I have no ready solution. Since accounts have just one password, you might try this: - click to settings>privacy&security - click the savedpasswords and then showpasswords - on the entry for the SMTP server, rightclick and select 'edit password' to verify that it is correct. Outlook stores a unique passcode for incoming, but the SMTP entry 'should' be your regular password.