Hi

We just set up a new server 2012 standard r2 with exchange 2013, all brand new install and we can telnet to port 25 internally, but not externally.  We have connected the server to 2 different firewalls and experience the same issue so it does not appear to be a firewall issue.  Setting up smtp on port 26 appears to work, however port 25 is being blocked for some reason.  The windows  firewall is disabled.

any ideas would be appreciated.

thanks

This may be a silly question... Can you see the traffic traverse the firewalls? is it actually getting to the firewall? Is your company a small office (Thinking if your ISP is blocking port 25). That would explain why port 26 would work.

It also appears this article may be related to your problem...

https://social.technet.microsoft.com/Forums/en-US/bb033c35-df86-4d32-8458-bb306a110359/cannot-connect-to-port-25-externally-and-owa-is-not-working?forum=exchangesvrgeneral

• Edited by Josh Lavely 13 hours 58 minutes ago Added related article

best bet is to contact your isp and ask them if they are blocking access to port 25

yes, we have had an exchange 2007 server running on win 2003 for many years, through the same firewall, same isp, etc.  We have duplicated all of the firewall settings, and even trying it through a completely different firewall with no luck.

Most firewalls have some sort of monitoring or logging functionality that would allow you to see if the incoming packets are even making it to the firewall (filter for traffic on port 25, you could compare to traffic on some other port, 80 for example, as a control).

Also, what happens between the firewall and the Exchange server? Do you use 1 to 1 NAT? Has this been adjusted to target the new Exchange server?

Otherwise, yes, ask the ISP just to rule that possibility out. Would be quite a coincidence that they start blocking port 25 at the same time you move to 2013 but changes have to happen sometime.

Yes, mail is flowing properly to and from our old server on port 25.  We have had an exchange 2007 server running on win 2003 for many years, through the same firewall, same isp, etc 

The issue is unique to our new server.   We have duplicated all of the firewall settings, and even trying it through a completely different firewall with no luck.

Yes, mail is flowing properly to and from our old server on port 25.  We have had an exchange 2007 server running on win 2003 for many years, through the same firewall, same isp, etc 

The issue is unique to our new server.   We have duplicated all of the firewall settings, and even trying it through a completely different firewall with no luck.

You are able to connect internally, so that means the Transport Service is listening on port 25.  When a telnet command comes in Exchange doesn't differentiate between an internal or an external address.  It just answers the request coming in.  That being said, Exchange and Windows firewall seems to be ok.  Do you have any other software firewalls installed on the machine that might cause some conflict?

The problem is either you need to tell your ISP to allow port 25 on the public of IP of your Exchange Server, your firewall rule is incorrect (meaning either the NAT is incorrect or ACL is not configured properly), or your rule is connect and your firewall is not honoring it (while unlikely still possible).  

Best bet is to look at the firewall logs, if you see the request come in and get blocked ,the issue is at your firewall.  If you do not, then the issue is at contained to your ISP.

This may be a silly question... Can you see the traffic traverse the firewalls? is it actually getting to the firewall? Is your company a small office (Thinking if your ISP is blocking port 25). That would explain why port 26 would work.

It also appears this article may be related to your problem...

https://social.technet.microsoft.com/Forums/en-US/bb033c35-df86-4d32-8458-bb306a110359/cannot-connect-to-port-25-externally-and-owa-is-not-working?forum=exchangesvrgeneral

• Edited by Josh Lavely Monday, April 20, 2015 5:25 PM Added related article

Hi,

From your description, I recommend you check if your receive connector is disabled in your new Exchange server. If yes, I recommend you enable it and check if you can connect to port 25 externally.

For your reference:

https://technet.microsoft.com/en-us/library/bb125140(v=exchg.150).aspx

Hope this can be helpful to you.

Best regards,

the receive connector is enabled.

thanks.

turned out to be an issue on our sonicwall.. problem resolved.

• Marked as answer by Jo Bime 15 hours 48 minutes ago