Error SMTP (450). Recipient address rejected: User unknown in virtual mailbox table

Good morning to all,

My problem is the following:

I have two A and B domains configured in my Sentora panel, although the MX record of domain B points to another IP (the mailboxes are in another domain provider)

The domain A that has the full panel (web, dns, mail, etc.) is not able to send emails to mailboxes in domain B.

The error that shows me:
SMTP error (450): It was not possible to establish recipient "david.fernandez@xxx.com" (4.1.1 <david.fernandez@xxx.com>: Recipient address rejected: User unknown in virtual mailbox table).

I understand that I can not send emails because the mailboxes of domain B do not exist in my Sentora panel, but they exist in my other domain provider and apart the MX records point to another server.

How can I fix this so that my domain A can send emails to another domain B with the mailboxes in another site?

I do not know how to solve this ... I need help please!

Thank you very much!

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