Configuring Blocked Senders Policies

Document created by user.oxriBaJeN4 Employee on Sep 11, 2015Last modified by user.oxriBaJeN4 Employee on Apr 2, 2019
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A Blocked Senders policy restricts messages to or from specific email addresses or domains. It can apply to inbound or outbound messages, although is typically used to block inbound messages.

View the Policy Specificity page for more information regarding the order in which Mimecast applies policies to emails.

Usage Considerations


Consider the following before creating a policy:

  • Messages from blocked senders are rejected and logged in the Rejection Viewer
  • Blocked Senders policies override any configured Permitted Senders policies.
  • Blocked Senders policies override addresses allowed by individual users. For example, messages from a domain added to a user's permitted senders list AND a Blocked Senders policy are rejected.
  • The following default Block Sender policies are created during your Mimecast account creation, and cannot be changed by administrators:

    • An External to External Block Sender policy that prevents senders using your mail server as an open relay. For example, we only accept messages from addresses belonging to your internal domains. Additional External to External Blocked Sender policy cannot be created.
    • An exception policy with the option set to "Take no action". This allows addresses / domains known to your company and can be relayed to via your mail server. For example, a staff member that has left your organization, but their email address is being forwarded on to a different email address.
    • An inbound Blocked Senders policy that references an empty group. You can populate this group by adding email addresses / domains manually, or by using a Spreadsheet Import.


Configuring a Blocked Senders Policy


To configure a Blocked Senders policy:

  1. Log on to the Administration Console.
  2. Select the Administration toolbar menu item.
  3. Select the Gateway | Policies menu item.
  4. Select Blocked Senders. A list of policies is displayed.
  5. Either select the:
    • Policy to be changed.
    • New Policy button to create a policy.
  6. Complete the Options section as required:
    Policy NarrativeEnter a description for the policy to allow you to identify it.
    Blocked Senders PolicySelect whether to block the sender or take no action.
  7. Complete the Emails From and Emails To sections as required:
    Field / OptionDescription
    Addresses Based OnSpecify the email address characteristics the policy is based on. This option is only available in the "Emails From" section. The options are:
    The Return Address (Mail Envelope From)This default setting applies the policy to the SMTP address match, based on the message's envelope or true address (i.e. the address used during SMTP transmission).
    The Message From Address (Message Header From)Applies the policy based on the masked address used in the message's header.
    BothApplies the policy based on either the Mail Envelope From or the Message Header From whichever matches. If both match, the specified value the Message Header From is used.
    Applies From / ToSpecify the sender characteristics the policy is based on. For multiple policies, you should apply them from the most to least specific. The options are:
    EveryoneIncludes all internal and external users. This option is only available in the "Emails From" section.
    Internal AddressIncludes only internal addresses.
    External AddressIncludes only external addresses. This option is only available in the "Emails From" section.
    Email DomainEnables you to specify a domain name to which this policy is applied. The domain name is entered in the Specifically field.
    Address GroupsEnables you to specify a directory or local group. If this option is selected, click on the Lookup button to select a group from the Profile Group field. Once a group has been selected, you can click on the Show Location field to display the group's path.
    Address AttributesEnables you to specify a predefined attribute. The attribute is selected from the Where Attribute drop down list. Once the attribute is specified, an attribute value must be entered in the Is Equal To field. This can only be used if attributes have been configured for user accounts.
    Individual Email AddressEnables you to specify an SMTP address. The email address is entered in the Specifically field.
  8. Complete the Validity section as required:
    Field / OptionDescription
    Enable / DisableEnables (default) or disables the policy. If a date range is specified, the policy is automatically disabled when the end of the date range is reached.
    Set Policy as PerpetualIf the policy's date range has no end date, this field displays "Always On" meaning that the policy never expires.
    Date RangeSpecify a start and / or end date for the policy. If Eternal is selected, no date is required.
    Policy OverrideThis overrides the default order that policies are applied. If there are multiple applicable policies, this policy is applied first unless more specific policies of the same type are configured with an override.
    Bi-DirectionalIf selected the policy is applied when the policy's recipient is the sender, and the sender is the recipient.
    Source IP Ranges (n.n.n.n/x)Enter any required Source IP Ranges for the policy. These only apply if the source IP address used to transmit the message data, falls inside or matches the range(s) configured. IP ranges should be entered in CIDR notation.
  9. Select the Save and Exit button.


See Also...


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