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I installed hMailServer on Windows Server 2003 and somehow I can't connect to SMTP 25 port from all computers. When I run the following command, it connects successfully on some clients, but on others it doesn't.

telnet 25

I have added an exception to the Windows Firewall for 25 port, but this does not seem to help.

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closed as not a real question by Ward, mailq, Scott Pack, Massimo, MDMarra Dec 14 '11 at 2:42

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center.If this question can be reworded to fit the rules in the help center, please edit the question.

Any local firewall installed on the workstations? – Vick Vega Dec 12 '11 at 20:25
I turned off firewall but it still doesn't connect. – ihorko Dec 12 '11 at 20:30
Are you using an antivirus on these clients (I hope you are)? Some of them (notably MCAfee) block outgoing SMTP connections hoping to deter worms. – Massimo Dec 12 '11 at 20:36
@ihorko - you have failed to answer the most basic question required for anyone to assist you in troubleshooting: What is different between the working machine and the non-working one? (Network/Location? Software installed? Settings? etc.?) – voretaq7 Dec 12 '11 at 21:21
And the Lord spake from on high and proclaimed "Thou shalt use a sniffer to see what is failing." – Zoredache Dec 12 '11 at 21:22

If people want to send mail on port 25, they should be connecting to their mail server, not yours. Port 25 is still occasionally used for internal mail submission, though it really shouldn't be. But it's primarily for one mail server to contact another for inter-domain mail relaying.

Why are ordinary users trying to connect to connect to your mail server on port 25? Port 587 is for remote mail submission.

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You've given little detail, so any answer is just a stab in the dark. That said, here's mine:

If it's not blocked by a firewall ACL, it's probably blocked by anti-malware. McAfee labels this "Prevent Mass Mailing Worms from Sending Mail" in the Access Protection section. Chances are, other AVs have a similar configurable setting.

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Yes, I have Comodo Antivirus, but why it doesn't block all requests – ihorko Dec 12 '11 at 20:41
I'm not saying with any certainty that it's your antivirus, but it's possible that it's configured differently on some workstations. Really, you haven't provided enough details for anyone to make any real educated guesses. – MDMarra Dec 12 '11 at 20:43
Ok, what details you need? I don't know what details should I provide – ihorko Dec 12 '11 at 20:46
@ihorko Any relevant log entries, procmon or netmon traces, you know...the troubleshooting that you should have done before you asked the question. – MDMarra Dec 12 '11 at 20:47
on localhost everything works perfect, or you mean run netmon on pc's where I can connect? – ihorko Dec 12 '11 at 21:01

I figured out. It's because on pc's where it doesn't connect, ISP blocks 25 port

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This is an incredibly common situation in the modern world. There is even a whole separate RFC ( & port (587) for handling this :-) – voretaq7 Dec 12 '11 at 22:25
There is no reason an ordinary user should ever be connecting to your mail server on port 25. Port 25 is for one mail server to connect to another mail server with which it has no previous arrangements. – David Schwartz Dec 13 '11 at 2:23

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