can you upload the attachment to www.virustotal.com and test with 40+ malware scanners
No because I would have to save it to my laptop first. And I don't want to do that. Whether or not the attachment has a virus or not is not the point ... the point is occasionally an email gets through without being scanned.
what mail account is the one not scanned?
my info@weblinksonline.co.uk email address is not being scanned when it has attachments

All of my email accounts are being scanned 99.999999999% of the time

Occasionally an email with a zip attachment is received that appears not to be scanned because it does not have the Avast message
99.999999999% of the time the Avast message is on the received emails.