SMTP Problem

[piwvh]

I have a vps with Centos 6.5 and postfix installed. When I want to connect to a smtp server like google or mailgun, I get the error 502 command not implemented.
I asked about it and people said it is because of CopFilter.
http://serverfault.com/questions/640357 ... mplemented
I wanna know is it true? And if it is, what should I do? I have not installed CopFilter.

And this is what happens:
[root@mail ~]# telnet smtp.gmail.com 25
Trying 74.125.196.108...
Connected to smtp.gmail.com.
Escape character is '^]'.
220 smtp.passthru
HELO
250 smtp.passthru
STARTTLS
502 Command not implemented

[ShelbyGT500]