Can't open port 25 to SBS2003 - URGENT!!

Im having a serious problem here and need help urgently!!

Im sitting at a new customer where I have reconfigured their Small Business Server 2003.
Problem was that they have never used the Exchange email but were using a mail hotel of the ISP.

I have changed the DNS so it now points directly to the server.
I have verified that this is functioning.

The server was originally configured with two NIC, one of the NIC's pointing to the router (Zyxel Zywall5).

I have disabled this NIC and reconfigured the firewall to forward SMTP, HTTP, HTTPS to the server.

When I look at the firewall everything seems ok.
HOWEVER I can't get through to the server on SMTP from the outside.

When I try to Telnet the server on port 25 from the outside I get an error telling me that I could not get a connection.

When done from the INSIDE of the LAN Im allowed access??

I belive this to be a router issue but I cant figure out WHAT?
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on your router, have you configured a port forwarding for TCP/25 to the internal IP address of your server ?

Please also check that your ISP allow port 25 ! A lot of ISP are blocking this port to avoid spam server or badly configured server on their network, so preventing their IP addresses to be blacklisted !


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Krzysztof PytkoSenior Active Directory EngineerCommented:
I'm not a big expert in firewall technology, but why do you need SMTP 25 from outside? I think you need POP3 110 to receive e-mails?

But I could be wrong :)

pop3 (tcp/110) is one of the protocol used to retrieve email. Mail delivery between servers is using port TCP/25.

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Shreedhar EtteTechnical ManagerCommented:

- Run SBS 2003 Best Practice Analyzer tool and fix the errors reported.

- Do run Configure E-mail and Internet Connection Wizard once.

Hope this helps,
Shreedhar EtteTechnical ManagerCommented:
- Check this ISP to see does the port 25 traffic is allowed by them for you public ip address.

Refer this article:

OhmitAuthor Commented:
Im calling the isp while writing :-)  I think this could be them blocking port 25.

I can confirm that smtp is forwarded through the router/firewall
Just a reccomendation, is an exceptional online tool to check mail server connectivity issues. What shreedhar reccomended is the best to do. I think you shouldn't have disables sxecond NIC, since SBS by default uses 2 NICs one for the LAN side and one for the WAN side.
OhmitAuthor Commented:
I can confirm that Port 25 was closed by ISP.  They opened up for 30 minutes ago but I still can't get through.  Maybe I shall be more patient :-)

There are a lot of sites like but problem is that they can only see that SMTP is closed. NOT why.

Microsoft uses the second NIC for internet connectivity.  When you use a hardware firewall/router there is no need for using it.
OhmitAuthor Commented:
Thank you all for your input.
I called the ISP and made them clear the blocking and everything was working  !!!
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