Exchange 2013 not receiving internal and external emails ..

Question

I have a coexistence of exchange 2007 and exchange 2013 ..2013 mailboxes where able to receive and send mails (internal and external) but suddenly the mail flow has stopped. 
Mail flow status
2013 to 2007 = OK
2013 to internet = OK
2013 to 2013 = OK
2007 to 2013 = FAIL
Internet to 2013 = FAIL 
incoming internet mails return the NDR below
Diagnostic information for administrators:
Generating server: mydomain.com
[email protected]
Remote Server returned '< #4.4.7 smtp;400 4.4.7 Message delayed>'
What could be a possible reason for this? 
Cheers guys ..
..forever is just a minute away*

Answer 1

Hi Richard,
Thank you for your question.
When there is a coexistence of Exchange 2007 and Exchange 2013, external email will be sent and received by Exchange 2013.
4.4.7 means message expired, message wait time in queue exceeds limit, potentially due to remote server(your Exchange server ) being unavailable.
If your organization has correct MX record in ISP. We could refer to the following link to check if MX record is correct:
http://technet.microsoft.com/en-us/library/aa998082(v=exchg.65).aspx
If we could telnet Exchange server by the following command: telnet mail.domain.com 25
If there is a receive connector on Exchange 2013 to receive Internet emails, we could create a receive connector to receive message from the Internet by the following link:
http://technet.microsoft.com/en-us/library/jj657447(v=exchg.150).aspx
If there are any questions regarding this issue, please be free to let me know. 
Best Regard,
Jim