Clive, From looking at your avast4.ini it appears you have not yet configured the Internet Mail Provider in the avast! On Access scanner. The complication going on here is that I suspect you have enabled the Exchange/Outlook Plugin and what we are doing here is trying to treat Outlook as a "generic" Internet mail client since that is how it is behaving with Mailmate.
Let's try faking it out by putting this section in the avast4.ini
[MailScanner]
ShowTrayIcon=0
UseDefaultSmtp=1
AutoSetProtection=0
PopListen=127.0.0.1:110
Trust=127.0.0.1
DefaultPopServer=dsl.pipex.com
Once you have done this save the file and try starting the Internet Mail Provider in the avast! On Access scanner.
If it starts and there are no port conflict messages shown by anything then the last thing to do is to go back into Outlook, change pop user name from csturnbull@dsl.pipex.com to ----> csturnbull#dsl.pipex.com@127.0.01
This should now put avast! in the chain. I imagine that with the Exchange/Outlook plug-in enabled you will actually have your mail in Outlook scanned by avast twice, once on the way in from the server (by Internet mail Provider before it is scanned by Mailmate) and the second time when it arrives in your Inbox by the Exchange/Outlook Provider. You probably can/should disable the Exchange/Outlook Provider-in but I do not know what additional services it provides Outlook users so lets check with avast! Tech Support on that.
I hope this works for you now. Hang in there, its a learning experience for me too and I am enjoying it, hope you are.
Sean D