When processing emails, Mimecast ‘explodes’ the email and 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. A Message Passthrough policy can be used to bypass these data optimization activities and deliver messages in their original raw file.
Consider the following examples:
- You can configure a Passthrough policy if, for example, your organization is developing software using .EXE files for updates and these files are held by Mimecast 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 has been completed.
- Other policies are still applied to a message if the Passthrough policy is configured. For example, if both a Message Passthrough and an Attachment Management policy is configured, the Attachment Management policy action takes precedence. If there are no other policies that apply, the raw file is delivered to the recipient.
Configuring a Message Passthrough Policy
To configure a Message Passthrough policy:
- Log on to the Administration Console.
- Click on the Administration menu item. A menu drop down is displayed.
- Click on the Gateway | Policies menu item.
- Click on Message Passthrough. 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 Provide a description for the policy to allow you to easily identify it in the future. Select Option
Select whether to explode or not to explode the message content.
- 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: Option Description 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. For multiple policies, you should apply them from the most to least specific. The options are: Option Description 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 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 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 "Always On" meaning that the policy never expires. Date Range Use this field to specify a start and / or end date for the policy. 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.
- Click on the Save and Exit button.