External users cannot connect to exchange

Hi There,

We have a several users located externally who connect to our exchange server using outlook and it has been working fine up until and for some reason several of the external users cannot connect to the exchange server.

I have tried all the basics, i.e. Ctrl + right clicking the outlook icon, and attempting to reconnect outlook to exchange to no avail. After reading up  a little more on this issue I saw a thread on a similar issue and tried the following:

> Modifying the host file (c:\windows\system32\drivers\etc) to include the external IP of the mail server and external mail server address

 > Modifying the outlook authentication settings from "negotiation' to NTLM and prompt for password.

Both of the above had no impact with resolving the outlook connectivity issue. If anyone has any tips or advise on this that would be greatly appreciated.  

Many thanks
Adma1Asked:
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Swapnil PrajapatiSr. System AdministratorCommented:
you can use microsoft exchange connectivity analyzer to see where it has problem.

Microsoft Remote Connectivity Analyzer
https://www.testexchangeconnectivity.com/
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Adma1Author Commented:
Microsoft Remote Connectivity Analyzer identified the credential failure issue has since been addressed.
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