As the title suggests, I have a group of users that I want to prevent from sending external emails.

I have created an Office 365 group, and added the required users to it. As administrator, I am the owner of the group, and therefore must be a member.

The problem is that I want the administrator account to be able to send external emails!

I could make one of the users the group owner, but then as owner they could add/remove users, which is obviously a security issue.

What is the best way to get around the problems I have described?


Use a mail flow rule through the Office 365 administrator portal.

Steps taken verbatim from: https://www.itprotoday.com/identity-access-management/how-block-users-sending-email-outside-organization-exchange-online

  1. Log on to your office.portal.com as the administrator
  2. Go to admin center
  3. Expand admin center and click Exchange
  4. Click "Rules" under "Mail flow" category
  5. Click "+" to create a new rule
  6. Fill in the rule name
  7. Choose "The recipient is located" from "Apply this rule if" drop down.
  8. Choose "Outside the organization" when a new window opens and then click OK.
  9. Click "More Options" to change other options.
  10. Choose "Reject the message with the explanation" from "Do the following" drop down.
  11. Type a message in the new window and click OK.
  12. Click Save.
  • That's what I'm creating the group for ... to list the users that I want to apply the rule to, or am I missing something?! Thanks! – 3-14159265358979323846264 Jul 27 '18 at 11:51
  • You might be able to add extra conditions - step 7. You may be able to add the group. You'll probably need an exception for the administrator. Personally I'd have a separate group that can be listed as the group admin and the members would be trusted individuals. Create your exception to use the group rather than the individuals - you can then add/remove users as necessary and keep your rules clean. – Kinnectus Jul 27 '18 at 11:55

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