SBS 2011 stopped sending and receiving external email

After an office move the SBS 2011 server has stopped sending and receiving external email messages. Internal messages are working.

Clients - SMTP mail from mail clients (on ports 587, 993) succeeds.
             - nslookup type=mx server 4.2.2.2 (or 75.75.75.75) show correct MX records
             - Telnet to server first will get an unrecognized command on a ehlo or helo, but then  will succeed on 2nd try.
            - ping to server has 35% loss with IP and DNS
Server - Email stuck in Exchange queue get error: 451 4.4.0 Unable to connect
            - nslookup type=mx server 4.2.2.2 (or 75.75.75.75) show correct MX records, but receive some timeouts

I have added DNS forwarders for our ISP into DNS service
I have added External DNS Lookups servers into Exchange.
I have cleared DNS server / service cache.
I have flushed DNS via ipconfig

Send connectors are using DNS for MX and External DNS Lookup.

At a loss for resolution. Seems extremely odd.
MEcadamsandersAsked:
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Patrick BogersDatacenter platform engineer LindowsCommented:
Hi again,

I need to ask again here, can you telnet into the SMTP server that belongs to your ISP from within the network?
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MEcadamsandersAuthor Commented:
I can reach other SMTP servers, but not on port 25. I am not able to get out on port 25 from clients or server. Did you review my config? Is there anything in it that could be interfering with it? The ISP is Comcast in Chicago and they dont normally block port 25 for business class service. I will call now and check with Comcast technical support.
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David Johnson, CD, MVPOwnerCommented:
check your site @ mxtoolbox.com, comcast may have to enable a smarthost for you.
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MEcadamsandersAuthor Commented:
I used DNS Stuff to check incoming during setup. IT did not work.
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Patrick BogersDatacenter platform engineer LindowsCommented:
Did you call Comcast technical support to verify if they allow port 25?
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MEcadamsandersAuthor Commented:
Thanks for keeping the troubleshooting process honest. I was so tired, and convinced this couldnt be the issue. It turns out that Comcast does place these business class modems in residential installations. When they do, they lock down port 25 in both directions. And the main technical support department cant escalate the issue. You must call Comcast Security Center for resolution. They place the resolution in a queue and it randomly started working.
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Patrick BogersDatacenter platform engineer LindowsCommented:
Great! thank you for posting back your findings.
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David Johnson, CD, MVPOwnerCommented:
It turns out that Comcast does place these business class modems in residential installations

Knowing Comcast it is residential class modem in business environment..
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