Relay access denied

I'm configuring a new email and i'm getting this STMP message:
-  Relay access deniedts

220 xxxxxxxxxxxxxxxxxxx ESMTP Postfix
HELO yyyyyyyyyyyyyyyyyyyyyyy
250 ns348267.ip-37-187-253.eu
mail from: pedro@yyyyyyyyyyyyyyyyyyyyyyy
250 2.1.0 Ok
rcpt to:<pedro.ferreira@new_domain.com>
454 4.7.1 <pedro.ferreira@new_domain.com>: Relay access denied

The other domain works just fine (it's a primary domain), i tried to add a new primary domain with this domain but it's still the same.

Do you want me to share some files or configures? Please let me know

you would need to provide more details explanation, probably the best would be to check on that with your server admin.