Policies - Configuring Attachment Block On Size Policies

This article contains information on configuring Attachment Block on Size policies, considerations for file size restrictions, handling compressed files, and steps for setting up and managing these policies in the Mimecast Administration Console.

Considerations

Consider the following before getting started:

• End users cannot release the attachments, as they are placed in the administration on-hold queue. Administrators can release attachments via the Administration Console. See the Releasing Emails and Attachments page for further details.
• Policies with individual file size restrictions are considered first, followed by the cumulative limits. For example, if an Attachment Hold on Size policy is set to block attachments over 10MB, and an Attachment Block on Size policy is configured to block attachments over 15MB, the following happens if a message is received with one attachment of 11MB and the second 5MB in size.
  • The 11MB attachment exceeds the limit in the Attachment Hold on Size policy and is sent to the administration On Hold queue.
  • The 5MB attachment is unaffected by the Attachment Hold on Size policy.
  • The combined size of the two attachments (16MB) exceeds the limit in the Block on Size policy, so all attachments are blocked.

This behavior is outlined in the notification generated when the policies are applied. This is dependent on your configured notification settings. For example:

Action Taken	Reason
Stripped and Linked	Contributes to exceed size policy of 10485760
Stripped (Blocked)	Exceeds size policy of 15728640

• For cumulative stripping, there is a minimum file size of 50kB before an attachment is stripped. For example, if a policy is set to block attachments over 10MB, and a message with five attachments with a cumulative size over 10MB is received, the policy is triggered and all attachments are removed.
• With compressed files (e.g. .ZIP, RAR, .7Z) the policy considers the unpacked size of a compressed file rather than the compressed size. For example, if a policy is set to block attachments over 10MB, and a .ZIP file is 4.5MB compressed but over 10MB when unpacked, the policy is triggered and the attachment is removed.

Configuring Attachment Block on Size Policies

To configure an Attachment Block on Size policy:

1. Log in to the Mimecast Administration Console.
2. Select the Gateway | Policies | Gateway Policies menu item.
3. Click on Attachment Block on Size.
4. Either select the:

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

5. Complete the Options section as required:

Field / Option	Description
Policy Narrative	Provide a description of the policy to allow you to easily identify it in the future.
Maximum Attachment Size (KB)	Specify a value in kilobytes for the maximum file size of all attachments in a message.

6. Complete the Emails From and Emails To sections as required:

Field / Option	Description
Addresses Based On	Specify the email address characteristics on which the policy is based. This option is only available in the "Emails From" section. The options are: 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. When both match the specified value, the Message Header From will be used.
Applies From / To	Specify the Sender characteristics that the policy is based on. For multiple policies, you should apply them 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: Enables you to specify a domain name to which this policy is applied. 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 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: 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: 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 "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 in which 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...

• Controlling Email Size & Attachments