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.
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:
- Log on to the Administration Console.
- Select the Administration toolbar menu item.
- Select the Gateway | Policies menu item.
- Select Blocked Senders. A list of policies is displayed.
- Either select the:
- Policy to be changed.
- New Policy button to create a policy.
- Complete the Options section as required:
Option Description Policy Narrative Enter a description for the policy to allow you to identify it. Blocked Senders Policy Select whether to block the sender or take no action.
- Complete the Emails From and Emails To sections as required:
Field / Option Description Addresses Based On Specify the email address characteristics the policy is based on. This option is only available in the "Emails From" section. The options are: Option Description 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. Both Applies 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 / To Specify the sender characteristics the policy is based on. For multiple policies, you should apply them from the most to least specific. The options are: Option Description Everyone Includes all internal and external users. This option is only available in the "Emails From" section. Internal Address Includes only internal addresses. External Address Includes only external addresses. This option is only available in the "Emails From" section. Email Domain Enables you to specify a domain name to which this policy is applied. The domain name is entered in the Specifically field. Address Groups Enables 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 Attributes Enables 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 Address Enables you to specify an SMTP address. The email address is entered in the Specifically field.
- Complete the Validity section as required:
Field / Option Description Enable / Disable Enables (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 Perpetual If the policy's date range has no end date, this field displays "Always On" meaning that the policy never expires. Date Range Specify a start and / or end date for the policy. If Eternal is selected, no date is required. Policy Override This 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-Directional If 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.
- Select the Save and Exit button.