IP Blocked by Third Party DNS Host - Nov 2019

Known Issue

Date Logged	November 7th, 2019
Product(s)	Email Security Cloud Gateway, Policies
Status	Not Fixing

Issue

We have identified an issue where third-party DNS providers are occasionally blocking Mimecast DNS look-ups against their name servers, resulting in temporary delivery errors.
This could be for outbound emails to non-customers or inbound emails for customers who've configured their inbound routing by hostname.

This is a known limitation not on the Mimecast Product Team Roadmap to resolve.

Workaround

Where this issue occurs, we will:

• Attempt to solve it with the provider on your behalf.
• Share the name server information with you.
• Ask that you contact the affected recipient and report the issue to their DNS provider.

In the event we cannot resolve an external domain via DNS, we recommend you take the following steps while we investigate the issue further with the provider.

1. Log in to the Mimecast Administration Console.
2. Navigate to Policies | Gateway Policies.
3. Create a Delivery Routing Definition pointing to the IP address of the affected domain's MX record. The IP can be found by using:

• Command-line DNS query.
• DNS lookup tool on the web.

4. Create a Delivery Routing Policy scoped from Everyone to the affected domain, and apply the definition created in the previous step.
5. Navigate to Message Center | Message Delivery.
6. Select the messages being blocked.
7. Click on the Recalculate Delivery Route button.

By default, the messages are delivered based on the standard delivery retry schedule. If you want them processed immediately, select the messages and click on the Retry button. After a few moments, the messages will disappear from the delivery queue, indicating they've been successfully delivered.

For inbound mail, the customer can update the hostname in their existing inbound delivery definition to an IP address and recalculate delivery routes.