To authorize Microsoft Office 365 to send emails on your behalf you will have to manually add it to your SPF record. The SPF record mechanism used for Office 365 is:
If Office 365 is your only sender your SPF record will look like the below example:
v=spf1 include:spf.protection.outlook.com ~all
In order to DKIM sign your custom domain emails you will need to complete the following steps:
Creating the CNAME records
The CNAME records are used to map an alias name to the true or canonical domain name. In essence when you provision a new domain name in Office 365 you will need to create two CNAME records for it so that it points to your initial domain. Here is an example:
We will use example.onmicrosoft.com as our initial domain, also called the tenant domain. But we actually own example.com and after we provision it in Office 365 we need to publish the two CNAME records so that example.com points to example.onmicrosoft.com using the format below.
If you are one of Office 365 US Government Community (GCC) customers, the domainGUID method below will not work for you. You will need to use the proper MX value for your domain. Example:
selector1-<domain-key>._domainkey.<initialDomain> for the examples below. Use this article to find the MX record needed for your domain-key value.
Host name: selector1._domainkey.<domain>
Points to address or value: selector1-<domainGUID>._domainkey.<initialDomain>
Host name: selector2._domainkey.<domain>
Points to address or value: selector2-<domainGUID>._domainkey.<initialDomain>
In our example the CNAME records will look like this:
Host name: selector1._domainkey.example.com
Points to address or value: selector1-example-com._domainkey.example.onmicrosoft.com
Host name: selector2._domainkey.example.com
Points to address or value: selector2-example-com._domainkey.example.onmicrosoft.com
Please pay close attention to the domainGUID which does not use a full stop "." but a dash "-" instead. This is taken from the MX record of your custom domain, in this case example.com
The reason behind the two CNAME records is because Microsoft rotates the two keys for added security.
Enabling DKIM signing
Once you have added the CNAME records (two per domain) DKIM signing can be enabled through the Microsoft 365 Security admin center at http://security.microsoft.com/dkimv2
Check if DKIM is configured correctly
Why not use our free Investigate tool to swiftly verify your DKIM configuration.
For more information on how to configure DKIM in Office 365 please click on the button below.
Create a free OnDMARC account to test your configuration.