Hey - thanks for all the replies!
Yes, I have run the mail protection wizard.
No 'blue ball activity' upon opening an e-mail btw and takes no notice whatsoever of the eicar file - until I save it, at which point it goes mental! (In a good way.) I make that five different confirmations that mail is not being scanned - case proven, your honour.
Upon further consideration, I think my problem is slightly different to what I originally thought. I recently 'upgraded' to Windows 98SE. (The only reason for doing so by the way, was the need for full USB support - everything else I needed worked fine in Windows 95
). I don't think since then I've actually had mail scanning working, but I've been fiddling around with other stuff and only got round to checking properly yesterday. I won't bore you with all the details, but the situation as of today is that if I run the wizard in 4.5 I end up with settings as described by Techie101, but when I try to pick up mail I get the error message shown in the attached file.
To get mail collection I have to set up Tbird 'as if Avast wasn't there' (i.e. actual pop, smtp and user names settings in the account settings). I thought I had seen this recommended as a fix for such problems elsewhere in these forums - but of course it just means that I've bypassed mail scanning!
So, my question now becomes - What is that error message, and does anyone have a way to fix it (other than my current not-very-clever one of not scanning my e-mail)?
Thanks again for your help!