SMTP Port 25 is blocked - how can I open it?

We have just installed a new Small Business Server 2008 with Exchange 2007 four weeks ago. It has been working fine for the last couple of weeks.

But two days ago, my internet dropped out.  My ISP suggested I reboot the router.  Hey presto my internet worked.

Now today I realise I haven't been receiving emails since then.

I phoned the ISP who opened port 25.  I can only assume they closed it.

Still no inbound email.  

But outbound email works.  Also website hosted in my office on 2nd webserver works as does FTP on my webserver.  Port 25 is open on my router.

Telnet 25 ... no connection

Someone please help me analyse this problem.
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enigmasolutionsConnect With a Mentor Author Commented:
Wholly crap!  I fixed the problem... this is how... (you will not believe it).

About 7 years ago I was using Netgear FVS 318 routers, and they all had this strange problem where if you mucked around with the TCP/IP port mappings (eg adding/deleting/editing) then the router would randomly forget one of the port mappings.  To solve the problem you simply had to clear out all the entries and re-enter them.

Guess what!  This Netgear bug is still around in their latest DG834 routers.

Just now I managed to fix the problem by deleting the SMTP port 25 mapping and simply re-adding it (exactly as it was).  Totally illogical!

check with your ISP If they block SMTP traffic or not.
first I ran an smtp test on your server and yes port 25 looks blocked

however i tried to send email to and noticed that is your relay.

is your domain name ?
enigmasolutionsAuthor Commented:

FYI - I use trend micro's Hosted Email Messaging Service - which just filters our spam before it hits my server.  I was going to mention it.

Anyway I am still astonished at the solution to this problem.
enigmasolutionsAuthor Commented:
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