It appears your server does not see itself as a destination for the email it's receiving. .
I would verify the following items to start.
mydomain = somedomain.com
myhostname = mail.somedomain.com
mydestination = $myhostname, localhost.$mydomain,mail.$mydomain,$mydomain
mynetworks = 18.104.22.168/27 127.0.0.0/8
relay_domains = $mydestination
smtpd_recipient_restrictions = permit_mynetworks,check_relay_domains
post the output of postconf -n
for further assistance.