I have an issue I can’t figure out, and that is why postfix is constantly emailing itself, like it is stuck in an unstoppable mail loop?

I can see from the email log that the email is bouncing, because of an unknown user:

Jan 27 02:35:17 mydomain postfix/local.... to=<inquiry@mydomain.com>, relay=local, delay=0.01, delays=0/0/0/0, dsn=5.1.1, status=bounced (unknown user: "inquiry")

But the email exist and the email is used for sending out emails via a contact form on the website, and the email is hosted at Office 365.

I’ve figured out that there might be an issue with the website domain name and the email domain name being the same (externally set up at Office 365), so is there anyone who has experienced the same issue and how to correct it?

Is there anything in my /etc/postfix/main.cf file that should be different to prevent this?

smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination
relayhost = [smtp.office365.com]:587
myhostname = mydomain.com
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = all
inet_protocols = ipv4