Mail account and "admon" string

Hello, how are you?

Is there a problem with including the string “admon” in the name of an email account?

When I create an account starting with the string “admon”, the mail is always returned with the error message “550 5.1.1 admon***@domain.tld: Recipient address rejected: User unknown”.
No matter if the mail is sent from the server itself or externally.

If the string is not at the beginning of the mail, the error does not occur (for example, ***[email protected]).

Thanks in advance.