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On a rackspace cloud server, I opened up Putty and it WORKS if I do "telnet localhost 25" on the VPS, the postfix process is running as well

However, if I try to telnet remotely like "telnet domain.com 25" it doesn't work, I've tried "telnet domain.com 22" and it works.

C:\Users\Shane>telnet domain.com 25
Connecting To domain.com...Could not open connection to the host, on por
t 25: Connect failed
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1 Answer 1

up vote 3 down vote accepted

Your ISP is blocking port 25 outbound to all but their SMTP servers. They usually do this in order to prevent naive zombies from sending mail. They may open it if you call them up and ask.

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Better would be to configure postfix to accept mail from authenticated users on port 587, which most ISPs aren't blocking. –  DerfK Apr 1 '11 at 13:14

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