I signed up for a new Gmail account and after allowing less secure apps I was able to receive messages through Thunderbird, but I still cannot send them. Each time I attempt to, I get a Google popup message asking me to login and allow Thunderbird access to receive/send/delete messages. I click allow and then I'm hit with a message saying that the message could not be sent. I spoke with Google support and they confirmed that my settings are correct from their end (correct smtp settings, less secure apps allowed, etc). No sure what else I can try. I do have other Gmail accounts working through Thunderbird. However one of my "other" accounts is having the same issue in that it can receive but not send emails. That happened once I was forced by Google to update my password. I'm hoping that the solution will work for both accounts. Server name: smtp.gmail.com Port: 465 Authentication: OAuth2 Connection Securtity: SSL/TLS