I think you misunderstand.

In 5.0, all headers was prefixed withh:. That made it not possible to use other valid prefixes. So we should remove the automatic prefixing and tell the user that if they want headerh: foobar they have to add headerh: foobar. Just addingfoobar should not be enough.

I think the issue is, that make the bridge incompatible with all other bridges because headers have to be formatted in aMailgun way.

What's if I implement aFallBackTransport that use Mailgun and then fallback to Amazon in case or error or whatever? The original email can't have a header compatible with both formats.

Hm.. I was convinced that theh: was for arbitrary headers. But I see fromthe docs thatReply-To is such header.

I was convinced by the exact same sentence in their doc 😉

@Nyholm to me, that's a bugfix. The current deprecation is buggy

Thank you@jderusse.