Hi Zyndstoff,
The message hasn't appeared again, but as I said, the message had only been coming up when I first install Avast and initially run it. After getting that message I checked OE 'Advanced' and 'Accounts' and made sure that the SSL and TLS options were unchecked. I also deleted the 'ssl' accounts in Avast per Olduns advice.
I note that the 'ssl' account list has returned in Avast but the message hasn't appeared again, and the 'globe' revolves during incoming email so I assume it is checking them.