Sitecore doc Recipient repositories claims "The Email Experience Manager can use various sources of recipients to send email campaigns, including both the sources provided by Sitecore and your own sources."
Apparently, to do this, you would need to (1) create a custom recipient repository, other than the default XdbRecipientRepository, and then (2) get EXM to use your custom repository when sending emails. But I can find no clue how to do either of these things. Does anyone have links or tips to how to do this?
Our use case is: We need to send mailings to a couple of "internal" lists (all employees & all students). It would be much easier to just create recipient lists "directly", rather than having to create and manage xDB contacts for these mailings. It should also be much more performant, because the xDB contacts API runs very slowly.
This is Sitecore 8.2, EXM 3.5.
Edit: Multiple answerers have suggested that we use List Manager's "Import CSV" feature rather than do what I'm asking to do in my question, so I'll explain why we're not doing that:
"Import CSV" is an interactive manual feature of List Manager. We need to synchronize these lists automatically (daily), not just import them once.
We need to add recipients to these lists ongoing, not just import the lists once.
We need to modify existing recipient's properties when the source properties change, not just import new recipients.
We need to remove recipients when they're removed from the source lists, not just import new recipients.