I am embarressed to say I need to re-open this discussion. After the 3 weeks of being unable to send emails, suddenly the fog cleared and all resumed to normal as tho' nothing had ever happened.
After many weeks of sending emails without problems we turned everything off when the builders came to change the electrics. After 28 hrs or so I booted everything up, sent a few emails only to find my (new?) IP address was being blocked by CBL. (188.119.192.40) I have checked ALL internal IP addresses, I have deep scanned with Avast, I have used MS Security Scanner (deep) and all say no problems. I've done lookup and ipconfigs. If I go to the ISP I'm sure they'll say I am infected but I am sure I'm not. Is there any way of seeing if the ISP is provably at fault? I have one last trump card....a laptop I have not opened for 2 years, so if this sends blocked mails (if you see what I mean) then it has to be them, but how do I convince them? Help again please, famed avast !