E-mail receivers get a warning

Question

Since upgrading to snow leopard, when I forward or reply an e-mail message to a pc user, they get a warning message that the e-mail may be infected. Yet when I send a new e-mail message they do not get any warnings.
What could be wrong?

Answer 1

Thomas A Reed wrote:
I'd say that, coinciding with your upgrade, one or more of your PC friends have been infected with a virus, and when you reply to or forward a message with a virus attached, you are leaving the infected file attached to the new message. When you reply/forward, make sure that any attachments are removed.
There is an option in mail (Edit>Attachments) to send originally received attachments when replying to a message... *'Always Include Original Attachments In Reply'*. Enabling that would allow you sending, by default, a possibly infected file. I think that option also allows forwarding a possibly infected file. Unchecking that would (I'm thinking) be of some help to you, at least for a time.
FYI, my default is set to, *'Always Send Windows Friendly Attachments'*. I have not checked to see if this option also always forwards original attachments, but believe that it doesn't.
However I do recollect a previous issue with infected files. It was not recent though and since using IMAP and restricting mail through other means, I have not had this report from my friends lately.
Henry