Policies - Message Passthrough

This article contains information on configuring and using Mimecast Message Passthrough policies to bypass message processing, their impact on attachments, policy settings, and considerations for safe use to avoid security risks.

When processing a message, Mimecast explodes it and its attachments into the raw components, indexes the text, and recompiles the attachment based on the header information regarding the attachment type (e.g., mime or content type). If this is set incorrectly, attachment corruption may occur. Message Passthrough policies can bypass these activities and deliver messages in their original format.

Messages handled by a Message Passthrough policy don't have their content exploded and can't be exported from the Mimecast archive. However, our data ingestion team can provide these messages via a data exgestion request, and they can also be forwarded by an administrator with content viewing rights from the Mimecast archive.

Spam Scanning, virus scanning, and attachment checks are still performed on messages when a Message Passthrough policy is applied, but we advise using a bypass policy with caution. They could allow a new virus outbreak to go undetected while signatures are being updated and could negate the Mimecast virus Service Level Agreement.

Usage Examples

Consider the following examples:

• • • You can configure a Passthrough policy if, for example, your organization is developing software using .EXE files for updates, and Mimecast holds these files due to a Suspicious Message Structure check. Configuring a Message Passthrough policy will allow the files to be delivered to the internal user as intended instead of being held by Mimecast. This should typically only be created after testing with Mimecast Support.
    • If the Passthrough policy is configured, other policies are still applied to a message. For example, if both a Message Passthrough and an Attachment Management policy are configured, the Attachment Management policy action takes precedence. If no other policies apply, the raw file is delivered to the recipient.

Configuring a Message Passthrough Policy

To configure a Message Passthrough policy:

1. Log on to the Mimecast Administration Console.
2. Navigate to Gateway | Policies menu item.
3. Click on Message Passthrough.
4. Select from the following:

• • • Policy to be changed.
    • New Policy button to create a policy.

5.   Complete the Options section as required:

   Field / Option	Description
   Policy Narrative	Describe the policy to allow you to identify it in the future easily.
   Select Option	Select whether to explode or not to explode the message content.

6. 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 Return Address: 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).
Applies From / To	Specify the Sender characteristics the policy is based on. You should apply multiple policies from the most to the least specific. The options are: Everyone: Includes all email users (i.e., internal and external). This option is only available in the Emails From section. Internal Address: Includes only internal organization addresses. External Address: Includes only external organization addresses. This option is only available in the Emails From section. Email Domain: This enables you to specify the domain name for which this policy applies. The domain name is entered in the Specifically field. Address Groups: This enables you to specify a directory or local group. If this option is selected, click the Lookup button to select a group from the Profile Group field. Once a group has been selected, click the Show Location field to display the group's path. Address Attributes: This 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: This enables you to specify an SMTP address. The email address is entered in the Specifically field.

7. Complete the Validity section as required:

   Field / Option	Description
   Enable / Disable	Use this to enable (default) or disable a policy. If a date range has been specified, the policy will automatically be disabled when the end of the configured date range is reached.
   Set Policy as Perpetual	If the policy's date range has no end date, this field displays as Always On, meaning the policy never expires.
   Date Range	Use this field to specify the policy's start and/or end date.  If the Eternal option 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.

8. Click on the Save and Exit button.

See Also...

• • • The Gateway Policy Editor
    • Policy Basics: From / To / Validity