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Supports SPF Does Not Support DKIM


To create a DNS record, follow these steps:

  1. Update the SPF records for your domains with the information displayed in the application under SPF Record, as shown below:

v=spf1 ~all

  1. Log in to your Domain Registrar
  2. Update/replace each domain’s SPF record to specify Mimecast as the authorized outbound service
  3. If all email for your domains will be routed via Mimecast, remove all previous SPF records
  4. Other outbound sources for your domain might require a combined SPF record; In this instance, ensure you include the Mimecast “” entry before creating a mail flow connector; To determine what “xx” is, refer to step 1 above
  5. Optionally test your SPF record:
  6. Navigate to Platform/Set Up Your Outbound Email in the Connect Application
  7. Select your domain from the Record to Validate dropdown menu
  8. Click on the Validate button; One of the following messages will display:
  • A green tick confirms the SPF record is valid
  • A red exclamation point confirms the SPF record is invalid
  • Click on the More or Less links to view further information about the SPF record and toggle the display

Note: If you already have an SPF record, merely add the following before the ~all mechanism:

Mimecast utilizes an include mechanism during the set-up process. For example, the following scenario is the most common (global) and would pass SPF:

v=spf1 ~all

If you send email from IP for the domain “” and that domain’s SPF record includes and the IP address passes the SPF record, this mechanism will pass.

Moreover, Mimecast does not allow for a custom Return-Path address to be used, which is a designated email address where bounced messages are sent. By customizing a Return-Path, the ability to present customer emails in a more professional manner (i.e., removes the default third-party “on behalf of” designation) is achieved.

How to Set Up/Modify DKIM for Mimecast

To do this, create an Outbound Signing Definition. Once this definition is produced, it will inform you what needs to be added to your DNS record. For more information on implementing DKIM for Mimecast, click here and follow the “Set Up DKIM for Mimecast” path.

As a user of this outbound email provider, Mimecast customers are afforded DKIM signing because it supports this mechanism. By utilizing its self-service portal, you can manually set up DKIM at your convenience. Overall, Mimecast provides DKIM signing and self-service set up, resulting in a streamlined process.

DKIM/SPF Setup Highlights

The below sections highlight notable characteristics of setting up DKIM and SPF for this provider as well as highlighting advanced settings if offered by this Outbound Email Source.


SPF Include Tag Required

This outbound email provider uses an include mechanism to add this provider's IP space to your SPF. To get fully set up with SPF for this provider, you will need to take the provided “include” domain and add it to your SPF record. An example of an SPF record without an include tag is compared to one with the tag added below (the include tags added are denoted in bold).


Initial SPF Record:

HOST TEXT v=spf1 ~all


SPF record include added:

HOST TEXT v=spf1 ~all


This outbound email provider does not allow a custom Return-Path address to be set. 


Supports DKIM Signing

Yes, this outbound email provider supports DKIM signing.

DKIM Setup Process: Self-Service Dashboard

This email provider offers a self-service dashboard where DKIM records will be setup for the account. To get DKIM setup for this provider you will login to your account at this provider and proceed to the DKIM setup area.