Michael,
Yes, it sounds like the headers will be different, but I'm not sure how. We need more information about the high-scoring lines...
No help from the MailMarshal forums.... The staff basically said they cannot tell me what is causing the high score....
Indeed, most of the HeaderSus rules are created strictly by looking...well, at header patterns common in spam - meaning, we've received heaps of spam with that header pattern, almost zero legitimate e-mail, and have adjusted our definitions accordingly.
The best recommendation I could give, is to ensure, for one, that your messages adhere absolutely as strictly as possible to RFC 822/2822. For example, many webmail scripts send lower-case header fields, making them an obvious target. The information within SpamCensor is proprietary, primarily for the protection of our own customers - if we made it public knowledge every last item we look for to determine whether or not something is spam, it'd be quite simple for people to get around many of the checks, exposing our customers to the stuff.
If the recipient trusts the sender, they should whitelist the address - plain and simple. I can however, say that we look at a combination of things beyond *just* the X-Mailer being used.
That's about as much as we can say really. I don't know of an anti-spam software vendor on the market who's interested in sharing with people how to circumvent their filters. Your clients will need to contact the recipients, and/or the admins on the remote side. If the recipient has indeed opted-in to receiving the blocked message in question, we can help them out quite easily.
I will have to do some tests to see if ListMail, perhaps, changes the headers at dailymail as opposed to during "Send Email", although it shouldn't because it uses the exact same domail() loop process from admin.php... :S I may have time to do such testing later this afternoon (2pm now) or in the early evening.
What I really need is a test server where I can install Mailmarshal, SpamAssassin, etc. and take a look at how different ListMail messages fare.
This may be the only way....
Regards
