PS: My outgoing settings are: Port 465 Connection security: SSL/TLS Auth method Normal password (I don't see the OAuth option!!!!) UserName: my gmail account

For authentication I only see: No authentication, Normal password, Kerberos, NTLM. The error I get is: "Login to server smtp.GMail.com with username C*******@gmail.com failed".

Update: One step forward: I deleted my Outgoing account and recreated it. After this, the OAuth2 option appeared. (Note: If I switch to StartTLS the OAuth2 option dissapear so I have to re-delete and re-create the account). However, I still cannot send emails.

I just checked my working settings. The incoming port is 993 if using IMAP and Port 995 if using POP. The outgoing (SMTP) is 587.

Google show 486 if using SSL. or 587 is using TLS or StartTLS. Thunderbird's database shows port 465 and I now think this is wrong as Thunderbird has not supported SSL for years (it was obsoleted by TLS 20 years ago as a protocol.) Perhaps when Google changed their authentication process they tightened the ports they will accept. Try changing the port to 587. I have oauth on port 587 with STARTTLS

A good tutorial here: https://support.mozilla.org/en-US/kb/automatic-conversion-google-mail-accounts-oauth20 Still won't work.

Matt said

Try changing the port to 587. I have oauth on port 587 with STARTTLS

Hi I tried STARTTLS/587 as you recommended. I have the same issue: when I press Send Email, TB gets stuck as "Status: Sensing message..." dialog box. If I press cancel, I get

Sending of the message failed. Unable to authenticate to Outgoing server (SMTP) smtp.Gmail.com. Please check the password and verify the 'Authentication method' in 'Account Settings | Outgoing server (SMTP)'.

The problem is that the OAuth dialog box from Goolge (that asks me to log in) never appears. Notice that it appears for the POP (read emails) account. I think something is broken in TB.

Matt said

Try changing the port to 587. I have oauth on port 587 with STARTTLS

Hi Matt. I tried STARTTLS/587 as you recommended. I have the same issue: when I press Send Email, TB gets stuck as "Status: Sensing message..." dialog box. If I press cancel, I get

Sending of the message failed. Unable to authenticate to Outgoing server (SMTP) smtp.Gmail.com. Please check the password and verify the 'Authentication method' in 'Account Settings | Outgoing server (SMTP)'.

The problem is that the OAuth dialog box from Goolge (that asks me to log in) never appears. Notice that it appears for the POP (read emails) account. I think something is broken in TB.

Matt said

Try changing the port to 587. I have oauth on port 587 with STARTTLS

Hi Matt.

I tried STARTTLS/587 as you recommended. I have the same issue: when I press Send Email, TB gets stuck as "Status: Sensing message..." dialog box. If I press cancel, I get

Sending of the message failed. Unable to authenticate to Outgoing server (SMTP) smtp.Gmail.com. Please check the password and verify the 'Authentication method' in 'Account Settings | Outgoing server (SMTP)'.

The problem is that the OAuth dialog box from Goolge (that asks me to log in) never appears. Notice that it appears for the POP (read emails) account. I think something is broken in TB.

PS: I tried to use a different GMail account as Outgoing (so me "email1" sends now emails via "email2") and it works. This is why I think my gmail account/inbox is corrupted in TB.

It worked. It is either because I challenged my outgoing server to another gmail account and then back to the original account OR because I wrote "smtp.gmail.com" (ok) instead of "smtp.Gmail.com" (bad).