Mail server and vpn in the same server

In one of the last posts of How to Secure Email Server Against Hacking with VPN, I was trying to set up a vpn server(WIREGUARD) in the same server as the mail server(POSTFIX), the thing is that when I try to send mails i receive
The mail server responded:
5.7.1 [email protected]: Recipient address rejected: Access denied..
I don’t know why it is showing this error, I think it’s because in of this line:
-o smtpd_relay_restrictions=permit_sasl_authenticated,reject
I would like that my vpn ip could send mails.
The only workaround I’ve found is change this line to:
-o smtpd_relay_restrictions=permit_mynetworks,permit_sasl_authenticated,reject
and adding to in mynetworks parameter
It’s safe? could i make a change on another place that should work better or increase security?
Thanks for your time!

Just was a misconfiguration on my files!

VPN Files or postfix/dovecot files? out of curiosity.