This is what it says, your default Mail profile in Outlook.
Outlook requires a default Mail Profile that holds details of your email accounts and the location of your mail database. (A PST file if you are not using Exchange.) You can inspect your local Profiles in the Mail section of Windows Control Panel
X1 detects this profile and uses it as the basis of its own activities.
If you don't have Outlook installed, you are probably out of luck when trying to index PSTs. But if you have a bunch of PSTs that are not attached to a Profile, then you can add them "manually" in X1 or you can do what I do which is to create a "dummy" profile that has no email accounts related to it but that acts as a "wrapper" for any number of PST files. X1 then detects this Profile and makes the PST files accessible for you to select which bits to index.
You can use the Mail bits of control panel to do other useful things, like telling Outlook to put your PST files where you want them, rather than where some dunderhead at Microsoft thinks they should be.