I'm not sure what you're saying here, but here's what will happen if a user who was not included in a scheduled collection changes his email preference (assume weekly -> daily):

 * `unqueueUsersForEmail`: nothing will change as he wasn't part of a bucket (he had no mail scheduled)
 * `saveQueuedUserIdsForEmail`: He will be added to the daily bucket.
 * When we collect the daily mails, the user id will be in there. We will fetch his activity stream, notice there are no pending activities in there and drop that user for email.

i.e. we will not send an email to user who has no mail-worthy activities in his stream.