Gmail Delivery Failure - Zendesk

In september, my company had a trial with Zendesk mail client for managing our mail and we didn’t continue with the program. Two weeks ago, we randomly started receiving these delay messages that have the desk-mail domain in our email address domain.

First, we contacted Gmail support told them about the issue and they told us to check under our admin console POP/IMAP to check if there is forwarding set up and there is not.

Second, we contacted Zendesk to see if our trial desk-mail account was causing problems, and they told us that we no longer have an account with them. They even checked their backend to make sure.

Third, we contacted Apple Mail, and there is no forwarding that can be set up, so that is not the issue.

We think that it is an issue with Gmail and Zendesk, but no customer support can figure it out.

Screenshot

Do you know what could be issue here? Thanks in advance.