Targeted Threat Protection - Attachment Protect provides advanced security protection for file attachments in email. It uses a definition that can be configured to deliver messages using one of the following methods:

Configuration

To use Targeted Threat Protection - Attachment Protect, you must configure definitions, and attach them to policies for the different attachment scenarios. You can configure any combination of the modes, and apply to all users or selected users / groups. View the Configuring Attachment Protection Definitions and Policies page for full details.

When configuring Targeted Threat Protection - Attachment Protect, we recommend:

• Referring to the Attachment Protect Best Practice page for a list of optimal definition and policy settings. You must log on to Mimecaster Central to access this page.
• Setting up the configuration for a small group of users, until you're satisfied the settings work for you.

Considerations

• Files that are unreadable, encrypted, or greater than 100MB in size, can’t be processed by the sandbox. Instead, they are allowed through and are not scanned or held. You can use an Attachment Management policy to hold encrypted, unreadable, or large files.
• If either of the following conditions are met, no safe file is created. The file:
  • Can't be larger than five times the original size.
  • Can never exceed 30 MB.
• The maximum size of a file that can be transcribed by Targeted Threat Protection - Attachment Protect is 15 MB.

We recommend you create attachment policies to handle these files. Failure to do so means these files are placed on Administrator Hold. See the Managing Attachments Overview page for further details.

Dynamic Configuration

If an attachment protection definition's delivery method is set to "Dynamic Configuration", the following process is used.

1. A check is made to see if the sender's email address is on the end user's managed senders list.
2. If the sender is:
   
   • On the end user's blocked senders list, the message and attachment are not delivered.
   • Not on the end user's blocked senders list, regardless of whether it is on their permitted senders or auto allow list, the following notification is displayed.
     
     
3. The end user can click either:
   • Request Files: Safe versions of the files are released and sent to the end user.
   • Request and Trust: The original files are released and sent to the end user if they are considered safe, and the sender's email address is added to the end user's trusted list.
     
4. Either:
   • If the sender is not on the end user's permitted senders list, or has an auto allow policy, an auto allow policy is automatically created.
   • If there is an auto allow policy for the sender, a flag is added to it to ensure it is not purged after 120 days.

Supported File Types

Targeted Threat Protection - Attachment Protect provides protection across the following file types:

• All Microsoft Office file formats
• All Open Office file formats
• PDF
• Archived files in the following formats:
  • ZIP
  • BZIP
  • GZIP
  • 7ZIP
  • JS
  • RAR
  • TAR
  • LHA
  • LZH
  • XZ

Requesting a Blocked Attachment

When a message containing an attachment has been put on hold as a result of an Attachment Protection policy finding it unsafe, the recipient receives an email detailing what has happened. If they wish, the recipient can request the administrator to release the original attachment to the user.

Malicious Code in the Original Attachment

If an email attachment is found to contain malicious code, it is blocked and not sent to the recipient. Instead, the recipient receives a notification informing them of the block, and displaying details of the:

• Message
• Attachment
• Policy that blocked it.

Handling Messages Held as Spam

When a message comes in with the attachment, it immediately goes into the Targeted Threat Protection - Attachment Protect sandbox for immediate scanning. If it's to be held, it is sent to the spam hold for release. Depending on your Attachment Protection definition, you'll have access to download the original file from the sandbox once the message has been released along with the attachment.

Safe or Unsafe Files

The administrator has full control over what happens to blocked attachments. Whilst the recipient can request for an attachment to be released, it is the administrator's ultimate responsibility to allow this. They can release the:

• Message to the recipient.
• Attachment to the recipient.
• Attachment to the sandbox.