Exchange Server Log in connection details

Question

Hello,

I need help to clarify some issues, please assist. So, as we know, any user can log in to their Outlook account with Outlook desktop application from externally and internally. I need to understand these questions:

1. How does the exchange server know whether this log-in connection request is from external or internal? How differentiate it?
2. How we can block it log-in connection from external? PS. I tried to block it with -MAPIBlockOutlookExternalConnectivity parameter in Exchange Server 2019, but it did not work. Also, blocking with a firewall is not compatible with us.

Answer 1

Hello @Baylar_Ismayil ,

Nice to see you again~

To answer your first question, Exchange Server can differentiate between internal and external log-in connection requests based on the source IP address of the incoming request. If the source IP address is within the range of IP addresses that are defined as internal, the connection is considered internal. Otherwise, it is considered external.

Regarding your second question, since the command is not work, I recommend to look into different options to limit external access on user and protocol level (such as ADFS or CA or IPsec) to block external log-in connections to Exchange Server 2019. Thanks for your understanding.

Reference:

https://learn.microsoft.com/en-us/answers/questions/1094102/block-outlook-anywhere-for-external-users-on-excha?page=1#answers

https://www.codetwo.com/admins-blog/how-to-block-external-access-to-exchange-admin-center-in-exchange-2019-via-client-access-rules/

Please Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.

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