Thanks. Hmm. Not sure I understand. 127.0.0.1 should also be wrong, or not?
I mean, when DeltaChat, using an e-mail@some-domain.fqdn says hello to the mail server it should say EHLO some-domain.fqdn or something, right? DeltaChat is not running on the server, so why would it say EHLO with the loopback address?
I still don’t have a good understanding of e-mail protocol. So maybe I am wrong.
Edit: Okay, probably I am wrong.
Thanks for informative comments in that issue: HELO "localhost" rejected (smtp and submission port) · Issue #1847 · deltachat/deltachat-core-rust · GitHub