If the server is up and running but users cannot send or receive any email, follow the steps:

 

 

Steps:

Get the last error:

Get-queue | fl

Look for “LastError” in the results.

 

 

 

 

If you are getting error:

[{LED=451 4.4.395 Target host responded with error. -> 451 5.7.3 Cannot achieve Exchange Server authentication};{MSG=};

 

Means that maybe the authenticated certificate is not installed or somehow corrupted

 

Fix:

Get-ExchangeCertificate

 

Look for “CN=Microsoft Exchange Server Auth Certificate”.

Copy its “Thumbprint”

 

Enable-ExchangeCertificate -Services SMTP

And paste the “Thumbprint”

 

 

The server should be up and running in few mins after.