Policies - Permanent MX Resolution Failure

This article explains how to configure the Policy for Permanent MX Resolution Failures.

A threshold of delivery attempts can be specified for Permanent MX Resolution Failure policies. In the event that MX resolution by Mimecast Message Transfer Agent (MTA) results in a permanent failure after the threshold is reached, an outbound message will be hard-bounced. Under the Bounces section, you can view Bounced Deliveries. 

There are two types of bounces:

• Hard bounces: The recipient server has rejected the communication.
• Soft bounces: The MTA has reached the final retry.

Usage Considerations

Consider the following before getting started:

• Permanent MX Resolution Failures are typically observed for non-existing/unknown domains. To check if MX resolution for a domain is likely to result in a permanent failure, you can use free online tools like MX Toolbox.
  • If the transcript option reports there was NO_ERROR, even when reporting a time-out, the domain does exist.
  • If the transcript reports there was a NAME_ERROR, it is likely that a permanent failure was encountered, and the domain is unknown.
• By default, the Mimecast MTA issues a delivery warning notification to the internal sender of a message if delivery fails to the recipient server after six attempts. This equates to one hour after sending. If the Mimecast MTA can't deliver a message in 30 delivery attempts, which equates to 4 days after sending, it issues a delivery failure notification to the sender. Such a retry cycle is common for MTAs to cater to transient issues.
• If delivery fails, you can instruct the Mimecast MTA to take items out of the outbound delivery queue faster than the four-day period. This is achieved by using a Permanent MX Resolution Failure Policy, but only if the recipient domain is truly unknown (e.g., it hasn't been registered). This is useful when the internal sender has misspelled the recipient domain. By hard-bouncing the message earlier, the internal recipient will realize the mistake sooner.

Configuring a Permanent MX Resolution Failure Policy

To configure a Permanent MX Resolution Failure policy:

1. Log in to the Mimecast Administration Console.
2. Select the Policies | Gateway Policies menu item.
3. Click on Permanent MX Resolution Failure.
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 for the policy to allow you to easily identify it in the future.
Number of Delivery Attempts	Set the number of delivery attempts after which a message will be hard bounced, should MX resolution result in a permanent failure (typically observed for non-existing domains). Supported values are from 0 to 30.

6. 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. 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 for the Message Header From will be used.
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: 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.

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.