I have a lineone email address. They were taken over by Tiscali and then again by TalkTalk. I think the issue is getting the correct port and SSL. The port should be 587 which seems to be the default option for the outgoing mail server and SSL should be 'Yes' with a password. The password I have entered should be correct as I'm getting emails delivered.
I have checked the preference in the mail set up and in the description box have called it Lineone. When I check the preferences the outgoing mail server (SMTP) is calling it Lineone (Offline). I'm assuming there is therefore an issue with the actual server!