More importantly, viruses of late forge the sender, so innocent bystanders get the bounces & "you have a virus!!!" return messages.
I just sent a batch of email to various postmasters & registered domain contacts asking them to turn off that feature in their mail server antivirus until they can get them to discern between viruses that forge the sender and those that don't. The bounces we get due to infected customers & newsletter recipients is rivaling the viruses the last couple days.
JA