Headers missing

[dimejo]

E-Mails send by this adapter (and used in Plausible) are flagged as spam by some providers, as some headers like Date and Message-ID are missing. Please see my comment at the Plausible Discussions for a small explanation.

Unfortunately RFC 2822 and 5322 do not clearly comment on whos job it is to create these headers. But as some of the most used MTAs do not create missing headers by default they should be created by the client (MUA).

Further read:
https://en.wikipedia.org/wiki/Email#Header_fields
https://en.wikipedia.org/wiki/Message-ID

[ruslandoga]

👋 @dimejo

Thank you for reminding me about this issue -- I completely forgot about it 😅

I'll try to handle it in #54

[dimejo]

Thanks for the fast PR!