hey a got the same error when trying to send mails outgoing mi LAN:
Feb 8 22:12:19 myserver postfix/qmgr: 31E2DA8734: to=<firstname.lastname@example.org>, relay=none, delay=0, status=deferred (delivery temporarily suspended: Host or domain name not found. Name service error for name=gmail.com type=MX: Host not found, try again)
I think my /etc/resolv.conf is ok:
nameserver 18.104.22.168 (ISP DNS Server)
nameserver 22.214.171.124 (ISP DNS Server)
Something I noticed is when I stop the iptables service the mails are sent, but when I start the iptables service it doesnt work again..
ports 25 and 53 are enable in my firewall
what could be happening?