Message Passthrough Policies

Document created by user.oxriBaJeN4 Employee on Sep 12, 2015Last modified by user.oxriBaJeN4 Employee on Mar 27, 2017
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In certain scenarios, Administrators may want to bypass Mimecast's data optimization activities whereby the message content is exploded, or attachments saved under the single instance storage mechanism. The Message Passthrough policy can be used to ensure that certain emails are delivered as the original raw file and are therefore not affected by Mimecast.


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. For example, using either the mime type or content-type. If this is set incorrectly, attachment corruption may occur.

However, all Mimecast Policies are still applied to the email. If the Attachment Management Policies are applied to Hold or Deny the attachment, the email is placed in the Held queue. The Strip and Link feature is ignored. If there are no Policies that apply a Hold action, the raw file is delivered to the recipient.



Take the following example. Mimecast receives a Word document where the mime type (content-type) is specified as text/plain, however when the attachment is exploded and recompile it as a text/plain file, this would cause corruption of the Word document as the mime type is not correct. In this scenario, the Message Passthrough Policy could be used to ensure that the attachment bypasses this process.

What you need

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


Creating 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.
Select Option

Select whether to explode or not to explode the message content.

Definition required?