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Exchange 2013 - unable to recieve external emails

Posted on 2016-11-11
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Last Modified: 2016-11-17
Hi Experts, have an issue where we are unable to recieve any external email. We had an existing email server and we added a new Exchange server. All URLs match for both servers and so do the certs. Today we made a change to firewall and externals DNS since IP address of new Exchange server has changed and now we are not receiving any external emails

Internal emails and sending emails to external domains is working fine

TIA
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Question by:abhijitm00
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Expert Comment

by:Jason Crawford
ID: 41883903
Where is the current MX record pointing?
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Author Comment

by:abhijitm00
ID: 41883913
MX record points to Comodo Antispam gateway so there is no change there
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Expert Comment

by:Jason Crawford
ID: 41883919
Have you tried running a message trace on the Comodo?  It would be helpful to know if it's ever received by an Exchange server or if it dies at the gateway.

What server is the Comodo handing off to?
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Author Comment

by:abhijitm00
ID: 41883970
I am getting: Relay : exchange.domain.org:25
 Error code : 500
 Error message : SMTP host unreachable
 No entries on your request
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Expert Comment

by:Jason Crawford
ID: 41884163
Ok did you add a firewall ACL and NAT for the Comodo IP on port 25?
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Author Comment

by:abhijitm00
ID: 41884173
No there is no ACL for Comodo on the firewall. It is open to all IPs
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Author Comment

by:abhijitm00
ID: 41884185
Just want to recap - Existing server name - mail.domain.org. All URLs point to mail.domain.org on both Exchange servers. New server name is exchange.domain.org. But cert has mail.domain.org as primary and exchange.domain.org and autodiscover as SANs.

All external DNS for autodiscover, mail.domain.org (via CNAME) point to exchange.domain.org which has a new external IP. NAT to old server mail.domain.org is stopped. At this time Activesync, Autodiscover and Outlook Anywhere stop working. Sending emails externally and internally work so does recieving emails internally, what does not work is emails sent from outside.

Would this have anything to do with FQDN name on recieve connectors or SSL certs?
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Author Comment

by:abhijitm00
ID: 41884186
Also wanted to add to comment above that Comodo Antispam can't seem to connect to exchange.domain.org on port 25 although all firewall rules seem fine
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Assisted Solution

by:Jason Crawford
Jason Crawford earned 500 total points
ID: 41884189
In that case you should be able to test access through the firewall by going to canyouseeme.org while logged on to the server receiving email from the Comodo and specify port 25.  Either that or you can try sending an email with PowerShell while off the network:

Send-MailMessage -From sender@domain.com -To recipient@domain.com -SmtpServer exchange.domain.com -Subject 'Testing' -Body 'This is a test'

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If your firewall truly accepts all connections on port 25 that should at least make it to a Receive Connector.  While you're at it you should enable verbose logging on all Receive Connectors:

https://msdn.microsoft.com/en-us/library/bb124531(v=exchg.160).aspx
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Author Comment

by:abhijitm00
ID: 41884310
Ok made some firewall changes and email is indeed flowing to new Exchange server.

Autodiscover and Outlook Anywhere is connecting but only after creating a new profile by manually adding server name. I have changed all URLs to point to exchange.domain.org and removed mail.domain.org from external DNS.
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Expert Comment

by:MB Shaikh
ID: 41885176
Hi,

Once if you receive you external email at your Comodo Antispam gateway, then check your newly installed exchange server is accepting connections on port 25 from  Comodo Antispam gateway  vice versa  probably fire wall may be enabled on newly installed exchange server and in Comodo Antispam gateway you allow proper routing etc.

regards,
MB Shaikh.
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Author Comment

by:abhijitm00
ID: 41885452
Android and iPhones are not able to configure using autodiscover. If I manually setup profile using server name I am able to connect. Outlook anywhere is working correctly. How can I fix autodiscover for phones? Currently i have autodiscover A record pointing to external IP of exchange.domain.org. There is also a _srv autodiscover record pointing to website, should i change this to exchange.domain.org?
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Accepted Solution

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Jason Crawford earned 500 total points
ID: 41886632
Yes you only need public DNS record for Autodiscover.  The A record you currently have in place should be fine so remove the SRV.
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Expert Comment

by:Jason Crawford
ID: 41892398
Glad I could help.  Take care :)
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