How to block domains in Microsoft Exchange Online admin center?

Exchange users now allow users to block and reject unwanted sender domains and emails or even specific email clients. What this allows for is the user more flexibility in configuring extra spam protection in addition to certain types of filters that may be present on Exchange, in case any spam-related content goes through the systems made for spam protection. An exchange global or network administrative body can block the pass-through of certain types of email-based content from certain external domains or addresses to the user mailboxes using native protection software such as PowerShell.

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To block domains in Microsoft Exchange you need to create a new rule. Follow the steps below.

  1. Firstly, sign into Office 365 using your normal login details.
  2. Now go to the admin section using the app launcher (illustrated by nine dots).
  3. Under “Admin centers,” click on “Exchange.” You may need to click “Show all.”
  4. Under “Mail Flow” click on “Rules.”
  5. Next a command panel will show and here click on the “+” symbol.
  6. Then click “Create a new rule.”
  7. In the “name” box make sure you type out “Block Sender Domain.”
  8. Fill out the information panel with the domain you wish to block.
  9. Make sure “Rule mode” is set to “Enforce.”
  10. Then click on “Save.”

To assist prevent email spam from being forwarded to a user’s inbox, an administrator can utilise numerous Office 365 spam filter settings. If you apply the parameters given below, the Office 365 spam filter will be better equipped to stop email spam and prevent false negative messages. A false negative in this context refers to email spam or trash messages that are sent to a user’s inbox.

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Bulk mail blocking in Microsoft Outlook:

If the spam is mostly mass mail, such as newsletters or promotions, you may configure Office 365’s spam filter to prevent bulk mail. The administrator can accomplish this by employing transport rules to filter bulk email communications aggressively.

You can add additional conditions to limit the application of transport restrictions to certain receivers inside your company. The harsh bulk email filtering settings will only apply to a few highly targeted individuals, while the majority of your users (who primarily receive the bulk email they signed up for) will be unaffected.

  • In the Exchange admin centre, go to Mail flow > Rules.
  • Click Add, and then select Create a new rule.
  • Specify a name for the rule this can be the one stated above for rule.
  • Click More options then, under Apply this rule if, select the subject or body > subject or body matches the domain you want to block.
  • In the specified words or phrases dialog box, add some regular expressions commonly found in bulk emails.

You may configure your spam filter rules to add the sender address or domain to the spam filter’s sender block list or domain block list. Spam will be noted on emails from senders or domains on a spam filter block list.

All configuration parameters display on a single screen when establishing a new policy, however, when modifying a policy, you must travel through many panels. The settings are the same in both cases, but the rest of this method explains how to update a policy and access these options.

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Why would you want to block domains?

Domains have an effective approach in allowing you to link your Outlook platform with DNS approved domains. However, there may be certain times where you don’t require this service and therefore, will have the need to block their users from sending emails to domain names that they consider untrustworthy. Exchange makes this possible through the use of transport rules, also known as mail flow rules. You can use transport rules in Exchange on-premises as well as Exchange Online.

Another reason why you may wish to block a domain off exchange is spam based content. Spam is unsolicited electronic junk mail delivered in bulk via the internet or via any electronic message system.

Things to look out for when making a new transport rule

A misconfigured transport rule may easily result in your organization’s outgoing email being refused. Always test your transport rules in a lab first, and then apply them in test mode for a period of time in production to see how they affect things.

Blocking based on domain names does not always address the problem of an unsecured or untrustworthy email service. Many additional domain names housed on Yahoo email servers are not blocked by a restriction like the one above in the case of some mail providers like Yahoo. And who’s to say a trustworthy partner’s email system hasn’t already been hacked, or that confidential emails won’t be viewed by unauthorised individuals after they leave your company.

By forwarding an email to another address, such as a Gmail account, and then sending it to Yahoo from there, domain-based banning may be readily avoided.

In-depth step by step process: How to block domains in Microsoft Exchange Online admin center?

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Breakdown of steps:

  • First, you need to sign into Office 365 using your normal login details.

Use your details associated with your Office account for example email, Phone even your associated skype account.

  • Use the app launcher to navigate to “Admin”.

The app launcher is illustrated by nine dots on the top left side of the display. You need to click on this to access the Admin portal.

  • Under the Admin center click on Exchange.

In this example “Exchange” was pinned so it was on the main menu panel on the left if it isn’t for you. Click on “show all” and this will bring up the “Admin centre” and here you want to find and click on “Exchange.”

  • Then under “Mail Flow” click on “Rules”.

As mentioned earlier in the blog the rules section needs to be addressed properly as it may affect how the content of your Exchange account flows with different users.

  • Next a command panel will show and here click on the “+”.
  • In the “name” box make sure you type out “Block Sender Domain”.
  • Fill out the information panel with the domain you wish to block.

Finally, click on save to save the presets as default.

That’s it for this blog post — thank you for taking time out to read our content. Please feel free to email our team about how it went if you followed the steps or if you need more help with the questions we answered in this Blog.

Saajid Gangat

Saajid Gangat has been a researcher and content writer at Business Tech Planet since 2021. Saajid is a tech-savvy writer with expertise in web and graphic design and has extensive knowledge of Microsoft 365, Adobe, Shopify, WordPress, Wix, Squarespace, and more! You can connect with Saajid on Linkedin.

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