Configuring Email Size Limits Policies

Document created by user.oxriBaJeN4 Employee on Sep 12, 2015Last modified by user.oxriBaJeN4 Employee on Jan 16, 2019
Version 9Show Document
  • View in full screen mode

Email Size Limits policies allow you to set size limits for both inbound and outbound mail, including the cumulative size of a message and its attachments. Any messages that exceed the specified size are rejected with the reason "Message exceeds email size limit". This policy is useful to:

  • Conserve storage in your company's internal environment. 
  • Enforce limits to the size of emails allowed in and out of your organization. 
If you've Large File Send as part of your Mimecast subscription, this can be used to send messages that would otherwise not be sent because of an Email Size Limit policy.

Usage Considerations


Consider the following before creating a policy:

  • A default policy is created with your Mimecast account. The threshold set in the policy depends on which Gateway version your account uses:
    • Latest Gateway = 200MB
    • Legacy Gateway = 100MB
  • Size restrictions on your internal mail server should match the limit on messages allowed through Mimecast. For example if an inbound limit on Mimecast is applied at 20MB and the mail server is restricted to 10MB, we will accept an inbound email if it is between 10MB and 20MB, but won't be able to deliver it to your infrastructure.
  • We recommend understanding the different components that make up a message. See the Email Size and Attachment Policies page for full details.
  • The threshold must be set to the maximum transmission size you'd like us to accept. This functions the same as the "Maximum message size" threshold on a Microsoft Exchange Server.
  • The transmission and content encoding can add significantly to the total size of a message.
  • The Email Size Limits policy overrules Attachment Block on Size and Attachment Hold on Size policies.


Configuring an Email Size Limits Policy


To configure an Email Size Limits policy:

  1. Log on to the Administration Console.
  2. Click on the Administration menu item. A menu drop down is displayed.
  3. Click on the Gateway | Policies menu item. The Gateway Policy Editor is displayed.
  4. Click on Email Size Limits. A list of policies is displayed.
  5. Either select the:
    • Policy to be changed.
    • New Policy button to create a policy.
  6. Complete the Options section as required:
    Policy NarrativeProvide a description for the policy to allow you to easily identify it in the future.
    Maximum Email Size (KB)Specify the maximum size of the email in kilobytes.
  7. Complete the Emails From and Emails To sections as required:
    Field / OptionDescription
    Addresses Based OnSpecify 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 / ToSpecify the Sender characteristics the policy is based on. For multiple policies, you should apply them from the most to least specific. The options are:
    EveryoneIncludes all email users (i.e. internal and external). This option is only available in the "Emails From" section.
    Internal AddressIncludes only internal organization addresses.
    External AddressIncludes only external organization addresses. This option is only available in the "Emails From" section.
    Email DomainEnables you to specify a domain name to which this policy is applied. The domain name is entered in the Specifically field.
    Address GroupsEnables 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 AttributesEnables 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 AddressEnables you to specify an SMTP address. The email address is entered in the Specifically field.
  8. Complete the Validity section as required:
    Field / OptionDescription
    Enable / DisableUse 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 PerpetualIf the policy's date range has no end date, this field displays "Always On" meaning that the policy never expires.
    Date RangeUse this field to specify a start and / or end date for the policy. If the Eternal option are selected, no date is required.
    Policy OverrideThis 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-DirectionalIf 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.
  9. Click on the Save and Exit button.


See Also...