search mailbox. How to stop the background execution of an erroneous move mail command?

Question

PowerShell

Hello Khabrovites.

The following bug happened:
When testing the practical possibilities of the Search-Mailbox cmdlet, the following test case was created:
An email was sent to the source mailbox [email protected] with the subject:
Copy/move email test
To copy/move this email to the target mailbox [email protected] command was used:
Search-Mailbox [email protected] -SearchQuery 'subject:"Test mailbox copy/move"' -TargetMailbox [email protected] -TargetFolder "Inbox" -LogLevel full | ft DisplayName, Success, ResultItemsCount, ResultItemsSize

And this is where the fun begins :)
To the mailbox[email protected] , with a frequency of 3 minutes, letters began to pour in

Content like this:

What was done after:
* In the original mailbox "Yung Dmitro Leonidovich", the problematic letter was deleted
* The queue was cleared on the mail server according to the subject criterion " Test of copying / moving letters "
But the flow of letters does not stop.
Please tell me where to dig.
Thank you.

2021-04-08 Addition: Importantly
, the sender of these letters is a dear friend:
[email protected]a
The sender address can be changed in the settings, but I do not recommend doing this, because such an address is googled, although not a lot, but there is little information.