Block some users in my domain from sending emails to external domains

Question

I have a create a rule on the Exchange admin centre (EAC) https://www.codetwo.com/admins-blog/how-to-prevent-office-365-users-from-sending-emails-outside-organization/ but it is not working. This article has been issued in 2022 and I believe Microsoft add changing from time to time.

I hope someone would love to help me on how to create a rule to block of users either by listing them or make a Distrubition list for those users then apply the rule on them.

Answer 1

Hello, thank you for posting in Microsoft Q&A forum.

According to your description, I tested it in my own test environment and the results showed that there was no problem. The relevant steps of the specific test are as follows:

1. Open the Exchange Admin Center. Go to Mail Flow > Rules.
2. Click the plus sign (+) and select Create a new rule.
3. Give the rule a name.
4. In the Apply this rule if... section, select The sender is a member of... and choose the user or group you want to block.
5. In the Do the following... section, select Block the message ... and enter a custom message explaining why the message was rejected.
6. In the Except if... section, select The recipient is... and enter the domain you want to block the user from sending emails to.
7. Click Save to create the rule and set the status to enable.

This rule will reject any outbound emails from the specified user or group to external domains and provide a custom rejection message as shown below.

Therefore, it is recommended that you refer to the above steps to check or recreate it. In addition, the problem may also be caused by the mail flow rule priority. It is recommended that you increase the priority of this rule to see if it is effective.

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Answer 2

Thank you for your help.

I created the rule and it is working as it should be.