exchange 2010 - cannot send mail to another AD site

OK - I'll try to shorten this, as the infrastructure is rather complex.
This is a global company in the middle of transistioning to EXCH2010 from 2003 - in the process of going to EXCH2013

they have 20+ AD Sites, and around 10 of the sites have Exchange. Some are EXCH2010 only, others are being migrated to 2010.

On site were originally on 2003 - they had already installed 2010 server - I migrated pilot - tested ok, and then moved the remaining users. They've used it for a couple of weeks - when we suddenly noticed that they could not send emails to one of the other AD sites. Only on. Let's call it SITE B

So emails from SITE A to SITE B don't work
emails from SITE A to SITE C, SITE D, SITE E and so forth works ok
emails from SITE B to SITE A works
just mail flow from SITE A to SITE B won't work

What we've done is:
-migrated users to EXCH2010
-removed EXCH2003 routing groups
-removed EXCH2003 - but problem was there before we removed EXCH2003, if we look at the logs

how does the error show:
- emails isn't delived - cannot connect to remote host. emails stays for 2 days then error is sent to sender
- when testing telnet MAILSERVER-SITEB 25 - it gives a blank black window, where as testing another site - it gives the proper ESMTP response
- the SMTP SEND logs looks like this:
2014-06-30T00:12:20.048Z,Intra-Organization SMTP Send Connector,08D15F45B4E3A71C,2,10.20.1.30:15281,150.56.34.30:25,-,,Remote
2014-06-30T00:13:21.326Z,Intra-Organization SMTP Send Connector,08D15F45B4E3A74E,0,,150.56.34.30:25,*,,attempting to connect
2014-06-30T00:13:21.967Z,Intra-Organization SMTP Send Connector,08D15F45B4E3A74E,1,10.20.1.30:38851,150.56.34.30:25,+,,
2014-06-30T00:23:22.659Z,Intra-Organization SMTP Send Connector,08D15F45B4E3A74E,2,10.20.1.30:38851,150.56.34.30:25,-,,Remote

- What I've checked:
- the Exchange server is not present in anonymous connector on receving side
- Changed to self signed cert on both sites
- made sure time is correct on both site

I've been told that there is no FW between servers. The sending servers is in Africa - the receiving is in Englands coastal area --- But I will have to double check this

maybe a HELP! might be in order ---
hope you guys have som input, I may have forgotten some tiny detail somewhere, but I cannot see where -- thanks !
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Jakob DigranesSenior ConsultantAsked:
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Simon Butler (Sembee)ConsultantCommented:
Blank window means the traffic is being blocked somewhere. Simple as that.
Could be a restriction on the Receive Connector, could be somewhere closer like a firewall, AV product etc.

However if it was an Exchange configuration error, I would expect the connection to be made, so I would be looking outside of Exchange.

The only other thing to check would be basic networking, including subnet mask etc, to ensure that they don't conflict in any way.

Simon.
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Jakob DigranesSenior ConsultantAuthor Commented:
Excellent .... it's what I've thought of - but wasn't sure. Will be looking at network and firewalls ... sadly, that has to go through the Networking Dept - which then has to take this to the global company handling landlines for the rigs ... mass-emailing; here I come

Will give you an update ASAP :-)
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Jakob DigranesSenior ConsultantAuthor Commented:
just one other question; failing to establish START TLS due to incorrect time or certs, could that give this error in telnet?
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Simon Butler (Sembee)ConsultantCommented:
A blank screen do you mean?
No, because TLS is established after the initial handshake. You aren't getting a response so it isn't even getting that far.

Simon.
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Jakob DigranesSenior ConsultantAuthor Commented:
Thanks .... this was it. Finally got ahold of the company looking after radio links to rigs, they was awaiting feedback from our networking dept, which they never got. 1 hour later they let all traffic from mail server bypass WAN optimizer and everything worked.
The strange thing is that sometimes the queues emptied themselves and emails where delivered - for no good reason. so it was hard to sell this in as a networking issue.

But now it works. Thanks a ton !
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