Faffy, avast! handles multiply pop/smtp accounts with easy. Do not mess this with the 'default pop/smtp server' configuration of the avast4.ini file.
You can see examples:
1. in the Culpeper`s suggestion
2. in the help file (manually configuration of the email accounts)
3. in the 'Understanding avast4.ini file' forum that I started in the past but you can find it searching the forum.
If nothing this help you, oh, that will be a 'The Bat' problem and I do not use this email account. Sorry.