I'm having some strange problems with sending out emails.
I've run a number of tests using different From addresses, and some of them work fine, but others are rejected by the recipient mail server. Here are the results of 9 different From addresses:
firstname.lastname@example.org (same domain as site)
email@example.com (same domain as site)
They don't fail for all recipients - there are clear patterns about which succeed and which get rejected. Most of the main webmail services: gmail, yahoo, hotmail, etc are rejecting them. Lesser know mail servers (presumably with less stringent criteria) are accepting them.
Outbound Mail is set to mail().
Any one else had problems like this, or able to offer advice?