Use these settings: incoming IMAP outlook.office365.com, 993, SSL/TLS, OAuth2, email address; outgoing smtp.office365.com, 587, STARTTLS, OAuth2, email address. Same for POP, except incoming port 995.

On my Outgoing server screen, under Authentication method, I have the following choices on the drop-down selector:

No authentication Normal Password Encrypted password Kerberos/GSSAPI NTLM

No OAuth2.

Is the outgoing server smtp.office365.com? Anything that begins with smtp-mail won't work.

https://support.mozilla.org/en-US/questions/1417298#answer-1588949

smtp-mail.outlook.com. Changed it and now it seems to be working. Thank you.

Cannot transmit. Get message: Sending of the message failed. The message could not be sent because connecting to Outgoing server (SMTP) smtp.office365-com failed. The server may be unavailable or is refusing SMTP connections. Please verify that your Outgoing server (SMTP) settings are correct and try again.

There was a typo in my previous reply. The correct server is smtp.office365.com, not smtp.office365-com.

8/1/2024 Still not working...

A dialogue box says transmitting with an active response indicator but goes no further.

Do you have a VPN? What is the antivirus?

My VPN and antivirus are Norton.

What is the correct port number for the outgoing server setting?

Thanks.

For smtp.office365.com, the port is 587 with STARTTLS security, as shown above.

Disable the VPN while using email.

I had entered an incorrect value for the port. Also, turning off VPN did the trick.

Thanks for all your help.