Bounce of emails from emails with the same domain

Your software
My Mautic version is: La versión 4.0.1
My PHP version is: 7.4.25
My Database type and version is: 10.2.41-MariaDB-1:10.2.41+maria~bionic-log

Your problem
My problem is:

Sorry because my English is not very good, I hope you can understand and help me.
When I want to send a message to an email that has the same email domain that the mautic has configured, it bounces me.

The message that I get the error is: User unknown in virtual mailbox table

Has someone something similar happened to you?

Check out the following places for hints:

  1. System Logs
  2. mautic.error logs
  3. Your ESP to see if the messages are reaching them (what ESP are you using)

To be clear you are trying to send an email from to a recipient like and it is not being delivered.

Yes, that example is correct. That is happening to me. I will check those suggested places.
Sorry, but what is ESP?