I have a vps with Centos 6.5 and postfix installed. When I want to connect to a smtp server like google or mail gun, I get the error
502 command not implemented. Can anybody help me please?
This is the full story:
[root@mail ~]# telnet smtp.gmail.com 25 Trying 22.214.171.124... Connected to smtp.gmail.com. Escape character is '^]'. 220 smtp.passthru HELO 250 smtp.passthru STARTTLS 502 Command not implemented
I think the problem is “smtp.passthru” … What is that?!
Its presence here indicates that your VPS service provider is intercepting outbound SMTP traffic in order to filter it.
Typically Copfilter is used to run anti-virus and anti-spam checks on email, though it could be used for other purposes.
In other words, instead of reaching Gmail’s servers, you have connected to the firewall, and the firewall will decide whether to pass your email along. It could also do other things such as keep a copy of the email you send.
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