I am finding subscribers' ISP that use
Symantec_AntiVirus_for_SMTP_Gateways
very annoying esp. with these "delayed" type messages sent back to list-owners:
Your message with Subject: blah-blah-blah
could not be delivered to the following recipients:
[RFC822 address]
Please do not resend your original message.
Delivery attempts will continue to be made for 5 day(s).