Let's Encrypt certificate installation problem

[SistemasMabisy]

Hello,

I'm having a problem generating the Let's Encrypt certificate from the VestaCP panel and I wanted to check it out here to see if anyone would know how to do it.

Situation:
In the VestaCP panel I need to create different email accounts for different domains.
The owners of these domains have the web hosted on another web server that is not VestaCP.
In the VestaCP server that I am setting up, they will only have the email accounts.
The dns of the domains are configured as follows:
- www.domain.com -> ip another web server
- domain.com -> ip another web server
- mail.domain.com -> ip VestaCP server

Problem:
In the Vesta panel I create a user for each domain to manage the email accounts so that everything is not together.
With the user created, I add the domain "domain.com" with an alias "mail.domain.com". (I don't add "mail.domain.com" as domain because I don't want accounts like "[email protected]").

When in the domain "domain.com" I mark the option of SSL Let's Encrypt, it stays loading and does not get to create the certificate.

I understand that when generating the certificate it will be trying to verify the .well-known with the main domain "domain.com" which, since it is pointing to another server, cannot verify it and does not generate the certificate.

Is there a way to exclude the primary domain and check only the alias "mail.domain.com"?

On a server with a cPanel installation, with the same situation mentioned above, if it generated the certificate with Let's Encrypt.

Thanks in advance
Greetings