Creating / Changing a Blocked Senders Policy

Document created by user.oxriBaJeN4 Employee on Sep 11, 2015Last modified by user.oxriBaJeN4 Employee on Sep 15, 2016
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Blocked Senders policies are created to restrict messages to or from specific email addresses or domains. The policy can apply to inbound or outbound messages, although typically it is used to block inbound senders that a company doesn't want to receive email from. When Mimecast processes a message from an address in a blocked senders policy, it is rejected and logged in the Rejection Viewer.

Administrator created Blocked Senders policies override User Block policies. This means that a domain that has been added to both a Permitted Senders policy and a Blocked Senders policy will be rejected, as the Blocked policy is processed first.




By default, Mimecast will create the following Block Sender policies during your Mimecast account creation:

  • A policy that prevents senders using your mail server as an open relay. This blocks any external address originating from your authorized outbound from sending emails to another external address. For example, Mimecast will only accept emails from addresses belonging to your configured internal domains.
  • An exception policy (with the policy option set to "Take no action". This allows addresses / domains which are known to the company, and have been added as addresses that can be relayed to via your mail server. This could be for a staff member that has left your organization, but where their email is being forwarded on to a new email address. The policy from EXTERNAL to EXTERNAL Block Sender is created by default to prevent open relay out to another external environment. Administrators will not be able to make changes to this policy. A new Blocked Sender Policy can be created to override aspects of the EXTERNAL to EXTERNAL Blocked Sender policy. It is not possible to configure an additional EXTERNAL to EXTERNAL Blocked Sender policy.
  • A typical inbound Blocked Senders policy, which references an empty Group. The Administrator can populate this Group by adding either email address or domains manually, or using a spreadsheet import. Using a Group enables you to minimize the number of Block Sender Policies you have in place, reducing Administration overhead.  Instead, one single Block Sender Policy can reference a Group, which contains multiple addresses or domains.


What You'll Need


  • An Administrator Console logon with access to the Services | Gateway | Policies menu item.


Creating / Changing a Policy


To create a policy, follow the instructions in the Creating / Changing a Policy article, but using the following options:


Policy NarrativeProvide a description for the Policy to allow you to easily identify it in the future.
Blocked Sender PolicySelect whether to block the sender or take no action.


Definition required?



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