When sending emails, they return with the error '451 Temporary local problem - please try later.'

Hello, I've been experiencing an intermittent error for over 15 days when trying to send emails from my dedicated server with cPanel. The emails are configured in clients like Outlook, and emails are also sent from a PHP application authenticated via SMTP. In both cases, when the issue occurs, the emails are returned with the error '451 Temporary local problem - please try later' when attempting to send them. I have also tested from Webmail, and I get the same issue.

I checked the Exim logs, and the following error appears (I've removed the original IP and the email hosted on my server):

2024-11-22 17:18:02 H=(JUANPC) [0.0.0.0]:39400 X=TLS1.2:ECDHE-RSA-AES128-GCM-SHA256:128 CV=no F=<test@domainonthissever.com> A=dovecot_login:test@domainonthissever.com temporarily rejected RCPT <test@hotmail.com>: Could not complete sender verify

This same error occurs when emails are sent between the same email accounts of the domain hosted on my server and for all accounts and domains on my server when this intermittent issue arises.

The solution I've found is to restart the IMAP server from WHM. Once the service is restarted, everything works normally. This issue happens once or twice a day.

I already reported this problem to the data center that leases me the server and the cPanel license, but they told me it's a very unusual error, and they haven't been able to resolve it.

My server has the following cPanel and OS versions:

OS: CloudLinux v7.9.0 STANDARD standard
cPanel Version: 110.0.48

I tried to open a ticket directly with cPanel, as I had done on other occasions when I had issues, but now it tells me that support must be provided by the company that sells me the license.

Has anyone else experienced this error who can help me?