Hello, I have a standard gmail, not a work email. I have used OAuth2 settings as well as attempted app password setup. Both have the issue of being unable to send emails. I have deleted all Thunderbird user data, removed my e-mails, uninstalled Thunderbird, restarted my PC & installed a freshly downloaded version of Thunderbird, setup my e-mail using OAuth2 & the issue still persists. I have verified in Gmail that Thunderbird has access to send, receive, & delete emails on the correct Gmail account. I have recently had issues with my Gmail account while using Thunderbird. My issues are as follows: I can receive all my emails but I am unable to send any form of e-mail. My error is: "Sending of the message failed. The failed message could not be sent becausr connecting to Outgoing Server (SMTP) SMTP.GMAIL.COM failed" I am using the recommended IMAP settings & I have performed this to verify it's correct: Right click on gmail imap mail account name in Folder Pane and select 'Settings' select 'Server Settings' Under 'Authentication Method' change to 'OAuth2' then change the outgoing server info. In left pane at the bottom select 'Outgoing server (SMTP)' select the name of the gmail server click on 'Edit' Alter the Authentication Method to say 'OAuth2' click on OK click on OK IMAP Settings: Incoming Mail (IMAP) Server imap.gmail.com Requires SSL: Yes Port: 993 Outgoing Mail (SMTP) Server smtp.gmail.com Requires SSL: Yes Requires TLS: Yes (if available) Requires Authentication: Yes Port for SSL: 465 Port for TLS/STARTTLS: 587