Issue

You need to set up DKIM for deliverability with Marketo, but another system you use already has DKIM set up with the default m1 selector.

Solution

You can create a Support ticket to request a custom DKIM selector be created (usually m2) for use in the "From Email" field on Email assets. Let support know what selector you want to use, and the domain you're want it to apply to- this is the domain value used in email assets, so for example@company.com, the domain would be "company.com"

This will allow your existing integration to utilize the m1 selector, and Marketo can have DKIM under another domain.