System.Web.Mail header problem

[SFletch]

I'm using System.Web.Mail MailMessage and on the whole it works.

Unfortunately one email in five (varies wildly) contains the following text as the first line of the email..

"X-MimeOLE"

I've examined two emails, one good one dodgy and found the X-MimeOLE header to be missing from the dodgy email. It's always this line that appears.

I assume therefore that the header is not correctly formed.

Has anyone else ever come across this? Anyone have a solution!?

Many thanks.