I have some questions about custom mail headers
Does anybody know of any mailserver which deletes proprietary/custom headers when being transmitted to its destination?
Is there a header you can set in order to force a mail client to return a certain header when sending a reply to a message that has exactly this header?
Does a custom header always begin with
X- ? Is it safe to use others?
Is it generally discouraged to use custom headers? How else could I transmit information that doesn't belong to the body and shouldn't directly be seen by the user?
PS: I know there's a similar question but this doesn't fully response to this question.
Thanks and regards