Thanks, Para-Noid. I tried specifying the URL in the Exclusions list but I still have the problem. The error is ‘Trust for this certificate has been revoked’. The certificate information identifies the site/certificate as “*.pacific.net.au”. I added the URL as “http://pacific.net.au”.
I’m now thinking the URL Tab in the exclusion list is for websites - Avast automatically inserts the prefix ‘http://’. Hence the Mail Shield Security Exclusion error may not be art of the AntiVirus shield.