I configured nodeBB with the cloudron mail relay and the relayed-to server is within an internal network directly attached.

It seems that emails are denied by cloudron's relay when the From/Reply-To address nodeBB uses is from a domain that is not @apps.example.com but rather from @example.com.
I want to use this noreply on my second level domain because the "discard" functionality is already configured there.

The nodebb log looks like this; There is no request being logged on the relayed-to mailserver.

 error: Mail command failed: 550 Authenticated user forum.app@apps.example.com cannot send mail as noreply@example.com {"code":"EENVELOPE","response":"550 Authenticated user forum.app@apps.example.com cannot send mail as noreply@example.com","responseCode":550,"command":"MAIL FROM"}