Why a domain does not let you create co-domain

[rutame]

I had many troubles with one domain, this domain has not a co-domain for this reason the mail accounts dont work.
I think that main motive is because is the same domain name that server.

I say this for if useful for somebody.

Thanks you

Greetings

PD: I cant change the server domain name because bind fails is make the change.

[till]

I think that main motive is because is the same domain name that server.

No, thats not the case.

Please post the exact error message.