You want to set up a DKIM key on one of your domains or subdomains, but another service has a DKIM key already set up on the selector/domain combo.



Beginning October 2023, Marketo has upgraded it's DKIM feature to allow for a Custom Selector for DKIM Keys. 
Most Users will be able to utilize the prior default selector, m1, as their DKIM Key.  However, if another integration is already utilizing the m1 selector, a custom value can be used. Common ones seen are "m2", "a1", "mkto", etc.
It can be longer, but shorter is generally better
 image (21).png

Afterwards, you'll be able to validate DKIM  as detailed in documentation:


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