Logos thanks for your help.
I had under Avast, before the update, made the changes in security that the popup message had suggested, but it seems I had not done enough. While I had reversed those steps when I turned off the mail shield for outgoing emails, by following your clear guidance I have the shield on and mails coming and going.
I hadn't realised that the shield wasn't working previously.
Again thanks for your help.
Cheers
Vaelor