Email 501 5.1.7 error

I have saved the config.production.json file and I expected to be able to INVITE new users. But I get error 501 5.1.7

I am not using mailgun… I am using fastmail.

See screenshot og ghost interface and server.

Hey @lukas_Stojanov, from the screenshot it appears you’re missing a from address. Check out our documentation for how to add it: https://ghost.org/docs/concepts/config/#from-address