postfix issues how to revert to a pristine configuration

HI guys,

I'm using OMV2.0, where everything goes well but postfix notifications.
Before asking for help, I just would like to put postfix in the same configuration it cames from when OMV was installed.
I did the stupid thing to play with the config before doing any backup or correct explanations of what I was changing in the configuration.
What is the best path to do so? Should I do dpkg-reconfigure or is there anything to do prior that in order to not mess up config.xml ?

Cheers

Ben

Thanks a lot alas It didn't fix my issue.
I can send notifications when using IP of smtp.gmail.com not not when using "smtp.gmail.com"

/etc/resolv.conf and /var/spool/postfix/etc/resolv.conf both have same config

# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)


#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN


nameserver 208.67.222.222


search lan

and a dig shows expected results:

root@openvault:~# dig smtp.gmail.com MX


; <<>> DiG 9.8.4-rpz2+rl005.12-P1 <<>> smtp.gmail.com MX


;; global options: +cmd


;; Got answer:


;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 25041


;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 1, ADDITIONAL: 0


;; QUESTION SECTION:


;smtp.gmail.com.            IN    MX


;; ANSWER SECTION:


smtp.gmail.com.        259    IN    CNAME    gmail-smtp-msa.l.google.com.


;; AUTHORITY SECTION:


google.com.        19    IN    SOA    ns2.google.com. dns-admin.google.com. 118357610 900 900 1800 60


;; Query time: 45 msec


;; SERVER: 208.67.222.222#53(208.67.222.222)


;; WHEN: Mon Mar 28 17:57:06 2016


;; MSG SIZE  rcvd: 140

I even tried:

# postfix check
# postfix set-permissions
# postfix reload

Very strange...