What is the best way to test the validity of a comma separated list of email addresses in a dynamic endpoint attribute?

I'm looking for something equivalent to Microsoft Outlook, where you can enter some raw email addresses into the To: field, then click "Check Names", which resolves valid email address formats and also checks if they are in active directory.

In this case, we would need:

  1. Check email addresses are of a valid format (I know it would be too much of a stretch to check for valid domain and valid mailbox in that domain)
  2. Check the list is properly comma separated

It would be nice if there was an attribute data reference type (similar to the URI builder) who's job was to handle this formatting and validation.

Things to consider from my investigating:

  • the "test" function in the contacts module says: "Sending a test email for an endpoint configured to retrieve an email address from attribute is not supported."
  • If we cut and paste into a new Outlook email, it doesn't like the commas
  • I don't really want to send a full copy of my notification every time a recipient is added
  • I don't really want to be a recipient of every notification I test (especially if I'm testing the validity of the address list).
  • I like the dyanmic end point rather than a contacts group because I like sending 1 email to 20 recipients rather than 20 emails to 1 person. This way, everybody knows who's getting the notification and they can reply all to collaborate if they need to fix an issue that is shown from the notification.

If anybody's got any good ways of doing this, please let me know.