Two of my pals are on Virgin for their internet email and I regularly get messages rejected from them, but not from anyone else on the same distribution list who are with other ISPs.

Anything I can do to stop this? My virus software says my PC is clean, and it isn't spam I'm sending - it doesn't even have a logo or picture, it's just a text email.

Here's an example of the return header:

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed:

*******.******@virgin.net
SMTP error from remote mailer after end of data:
host inbound.virgin.net.cust.securehostedemail.com [64.97.204.30]:
554 5.7.1 Requested action not taken: Message was spam or contained virus

------ This is a copy of the message, including all the headers. ------