Undelivered mail returned to sender - Notification openmediavault

Hello,

I'm creating this post because I'm facing an issue with the notifications in openmediavault. I have configured the notification part in the settings correctly; when I send a test email, everything works fine. However, when I'm supposed to receive an automatic email (from fail2ban or SMART tests, etc.), I receive a message on my sending email address saying: "Undelivered mail returned to sender."

Any explanation? Any solution?

Thank you.

Update: I am now correctly receiving the email when someone logs into the web interface.

No one has any answers?