Which services sends SYSTEM type messags

[Mr. Smith]

Hi.
(just uninstalled Symantec AntiVirus, since I thought it might hassle with
my outgoing mails.)
I get a message from System Administrator telling me that a harmles Excel
workbook contains VBA code and can not be sent, when I try to send a mail
with the Excel workbook attached.

Which services can send SYSTEM type messages like that, and where do I set
the policy. The ISP is not the problem.

I'm not logged on to a domain.

Mr. Smith