I am getting the error: The mail server responded: 5.7.8 [TPG-A02] Authentication denied. User is banned from using SMTP AUTH due to previous abuse.
I have checked the smtp settings etc and even deleted the account (which was a big mistake because I lost all my folders). The ISP has confirmed that I am not blocked and the the port settings and everything is correct. I confirmed this by being able to send emails from my webmail inbox. How do I go from one day fine to the next unable to send? I did get some messages one day saying "undeliverable to" a whole bunch of random emails addresses that I did not send, so maybe that has something to do with it?
Alla svar (2)
The bad news is, I think, that you need to persist with your ISP/mail provider until you find someone who knows what they are talking about. The message is from the SMTP server and it is denying you access. I would take it that the recent spate of undeliverable messages, falsely giving your email address as the sender, had prompted someone to report your address as a spam source.
Most of my traffic from mozilla goes straight into gmail's Spam folders, I guess because there are idiots out there who subscribe, decide they no longer want the traffic and rather than sensibly unsubscribing, start marking all the stuff they don't want as Spam. So everyone else suffers when gmail's systems respond by treating all mozilla-related messages as Spam.
The webmail works fine because it uses a different server and different protocols. And spammers don't use webmail hosts to send, so there isn't the same likelihood of the webmail server becoming blacklisted itself, nor of it blacklisting your address.
There are 2 posts on this same subject by the same OP. https://support.mozilla.org/en-US/questions/1233232