Way to migrate a legacy email list rather than each user click click click...

Is there a way to admin Autoresponder other than the Autoresponder block?

We are in the process of converting a legacy website over to Drupal, so Autoresponder seems the way to handle the email lists. Just that all of the users have not been created in Drupal yet as Drupal is not officially live.

As well, some users might not be ever in the Drupal UserID list, but they might be signed up to receive emails.

How do we handle this sort of thing?

Thanks!