I created the Toonel SMTP and POP3 entries in mapping, but left the port at 25 and 110 as they were set by default (which would mean avast would redirect).
I tried modifying the Internet Mail provider, basically in the same way as for the addition of another proxy, by unchecking the, Redirect, Ignore Local Communication option and having set up the Outlook Express account details Server to 127.0.0.1.
Whilst Toonel reported the SMTP and POP3 status as active and x number of open tunnels open, nothing ever came through the tunnels, everything just hung.
So I don't know if avast redirection on the standard ports is happening before toonel so nothing happens or if I should check the Ignore Local Communication, but that would defeat the object of as the toonel traffic wouldn't be scanned.
Since I normally pre scan my email on the server (mailwasher pro) and filter spam, etc. at source, very little actually gets downloaded to my system/inbox. So I didn't expend much time trying other options to get it to work.
As you say there are very few who would be prepared for this amount of manual setup to get it working and that is with the added complication of having other localhost proxies to co-ordinate with.