Hello,

We use Exchange 2013 on Windows 2012. Since yesterday, we can't  send or receive emails to / from outside .
Internal email works.

How to diag/analyse the problem ?
Thanks for your help.

Nico

• Edited by nicopulse 14 hours 23 minutes ago

The best place to start is the NDR that the user receives when the message fails to go through.  That will give you an error message that can be used to troubleshoot.  The other place to start, were their any other changes on the network?  

More information is really required on this issue.

The NDR is a great place to start.  You should also check your MX records and make sure they resolve in DNS properly. Also try telnetting from to where your mx record points to from outside of your network and check your firewall.

Thank for your help. In fact, our external relay for spam was dead :)

Just curious that exchange dont deliver this information.

There's no way for Exchange to know that the external source of mail coming into your environment is down. it just sits there waiting for mail to be sent to it. 

If you were sending mail through it, I would expect you would see an issue in the message queues.