Error message “Mail Delivery System. Undelivered Mail return to sender ... "

If your email server details are entered correctly, the emails you send will also be sent.

The error message “Mail Delivery System. Undelivered Mail return to sender ... “occurs when something is wrong with the recipient.

For example, if a customer's e-mail address has changed or the e-mail inbox is full, an error message is displayed. Unfortunately we cannot do anything ourselves.
The solution is to check the e-mail addresses concerned and ask people whether their e-mail inbox is full.

As I said, the mails go out correctly. It's similar to the post. If you send a letter and the recipient has moved or changed their address, the letter will come back.

Another possible solution could be a missing SPF record at your mail provider or your domain.
You can find more information about this here:

> SPF record at the mail provider

Keywords: SPF settings, spam, email not working, outbox, outbox, cannot be delivered, outbox, confirmation email, undeliverable, email settings, email provider, Gmail, G-Mail, United Domains, domain settings, email Mail delivery, e-mail hosting