Host or domain name not found

[a***@gmail.com]

The first time I installed postfix.
I can not send a message.

/var/log/mail.log
Dec 18 12:33:38 ubuntu postfix/smtp[26810]: 047FEC6239: to=<***@gmail.com>, relay=none, delay=8345, delays=8324/0.02/20/0, dsn=4.4.3, status=deferred (Host or domain name not found. Name service error for name=gmail.com type=MX: Host not found, try again)


Looking to find the problem - DNS file resolv.conf.
I do not have in the system.

This is nslookup
***@ubuntu:~$ sudo nslookup gmail.com
Server: 127.0.1.1
Address: 127.0.1.1#53

Non-authoritative answer:
Name: gmail.com
Address: 173.194.32.150
Name: gmail.com
Address: 173.194.32.149

How to solve the problem?

[Lemat]

Dec 18 12:33:38 ubuntu postfix/smtp[26810]: 047FEC6239: to=<xxx gmail.com>, relay=none, delay=8345, delays=8324/0.02/20/0, dsn=4.4.3, status=deferred (Host or domain name not found. Name service error for name=gmail.com type=MX: Host not found, try again)
Looking to find the problem - DNS file resolv.conf.
I do not have in the system.

And that is the problem I guess.
You should have /etc/resolv.conf with (I guess):
nameserver 127.0.0.1
And if your postfix is chrooted it should have
/var/spool/postfix/etc/resolv.conf