[brightball]

That’s a huge security issue! Geez.

If anybody realizes you’re using that service they can immediately impersonate you.

[hda111]

The email standards explicitly allow everyone to impersonate anyone. That’s why you should use S/MIME and PGP.

[15characterslon]

That's not true. SPF and DKIM were explicitly made to prevent email forging by authenticating the server, and the server is responsible for authenticating the user.

Please name even a single major mail provider that allows to send emails with arbitrary "from" headers.

https://datatracker.ietf.org/doc/html/rfc7208 https://datatracker.ietf.org/doc/html/rfc7489

[brightball]

If you’re using DKIM to sign the outgoing message it’s a huge flaw if your service provider is signing other peoples emails with your key just because they included the domain. You authenticate to the server for a reason.