From and Reply-to mail headers are ignored

I decided to merge 🐛 Reply-to is ignored if the mail is sent by Webform Needs review into this issue because both solutions had too much overlap.

Allowing the from to be set can lead to quite a few unsent emails, as sparkpost requires you to use a verified sender domain

The reply to seems like a good idea though. Would love to see some tests though, to ensure we don't introduce any regressions 🤓✌️ Are you able to code up some of that?