We have a situation where a php program sends a confirmation email when customers make appointments using php mail.
We set the "from" address in php mail to a specific email address that is a REAL email address. The host overrides it with one of their own. I believe I know how to override the host from doing that.
Some of the customers do NOT receive the confirmation email. I think doing what I have indicated will fix that, but I don't know how to test it. Seems I need a lot of diversity in testers.