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RestrictExtRecips for Outlook 365
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Updated: 26-November-2019
See also: 
RestrictExtRecips for Outlook 2013/2016/2019
RestrictExtRecips for Exchange 2013/2016/2019


As you know, Exchange online limits the number of recipients (both internal and external) per message for each mailbox.
There is no way to limit the number of external recipients a certain group of people can send to.

If you run Outlook OWA or Outlook 365 on Windows or Outlook on Mac, RestrictExtRecips add-in will solve this problem.

Let's suppose an Exchange online administrator has created a distribution list named "RestrictExtRecips_2". Number 2 after underscore means that each member of this list cannot set more than 2 external recipients in his message. If a user adds 3 or more external addresses to the "To:" or "CC:" field then the message will not be sent and a warning notification will be shown.

The application is an add-in for Outlook 365/Exchange online.

Current version:



  2. As a user with exchange online administrator role log into exchange admin center. Create a distribution list [1] named RestrictExtRecips_2. To the "Notes" place the prefix "Non-restricted:" and the comma-delimited string of internal domains [2]. Example:


    Make sure you are a member of the distribution list 'RestrictExtRecips_2' [3]. Do not add more than 2 members to the list as you run the demo.

    RestrictExtRecips addin installation Picture 1

  3. Login to your Office 365 and select Outlook. Click "New Message" button. Select More actions at the bottom of the message.

    RestrictExtRecips installation picture 2

  4. Go to the bottom of the list and select RestrictExtRecips installation picture 3 Get Add-ins. Select My Add-ins. Scroll down and click Add a custom add-in.

    RestrictExtRecips installation picture 4

    From the drop-down list, select "Add from URL...". Place to the "Enter the URL of the add-in's manifest file:" field. Click OK button [1]. Now you'll see a warning message. Click Install button [2].
    Note that by clicking "Install" you agree with EULA.

    RestrictExtRecips installation picture 5

  5. Make sure that RestrictExtRecips is in the list. Click Close icon Close icon to close "Add-ins for Outlook" window.

    RestrictExtRecips installation picture 6


  1. Open OWA and create a new message. Insert 3 external addresses in the To: field". Populate the Subject: field. Click the Send button. 2 warning notifications will appear.

    RestrictExtRecips add-in testing Picture 1

  2. Note that you can place any amount of external recipients into the "BCC:" field.


  1. Login to your Office 365 and select Outlook.
  2. Click "New Message" button. Select More actions at the bottom of the message.

    RestrictExtRecips uninstallation picture 1

  3. Go to the bottom of the list and select RestrictExtRecips installation picture 2 Get Add-ins. Select My Add-ins.
  4. Click on "My Add-ins" and click three dots icon near RestrictExtRecips add-in
    and select Remove

    RestrictExtRecips uninstallation picture 2

   RestrictExtRecips has been tested with:

   RestrictExtRecips does not work with:


About this demo version


Q. Can I restrict the number of internal recipients too?
A. Yes. Delete the prefix "Non-restricted:" and the comma-delimited string of internal domains from the Notes field of restrictextrecips_XX group. After that the addin will restrict both internal and external recipients.
RestrictExtRecips add-in F.A.Q. picture 1

Q. Will it help us be more GDPR compliant?
A. Yes. As you know, sharing the email addresses with other recipients is a breach of GDPR regulations - have a look at this article: 5 Ways Your Emails Could Breach GDPR. With RestrictExtRecips you can force users to use "BCC:" instead of "To:" and "CC:".

Q. How can I define the number of external recipients?
A. This number is defined by the name of the distribution list.

Q. What happens if the mailbox is a member of several "RestrictExtRecips_XXX" distribution lists?
A. The lowest number has priority over others.

Q. May I hide "RestrictExtRecips_XXX" distribution list from address lists?

RestrictExtRecips add-in F.A.Q.Picture 1
A. No, don't do that. As soon as you you hide a distribution list, it becomes invisible for RestrictExtRecips add-in.

Q. I've created 2 DLs: RestrictExtRecips_3 (10 members) and RestrictExtRecips_10 (15 members). How many licenses should I buy?
A. 15 ones.


Licensing policy: the product is licensed on a per-computer (sometimes called per-workstation) basis.

Number of licenses Individual price Your payments will be securely processed by Share-it
€ 35
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From 10
€ 32
Site license
€ 1800
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Enterprise license
€ 7000
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All transactions are securely processed by our external registration providers.

Site license covers a single organization in one location (building complex). If you purchase a site license, you may use the program in an unlimited number of your company's computers within this area.
Enterprise license covers all computers of single organization world-wide. If your company has many branches even with thousands of machines, Enterprise license covers them all.

If you are running Outlook on Windows Terminal Services or Citrix, you should purchase a Site license for each Citrix/TS server.

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