Scheduled mailing doesn't update recipients before sending.

The basic issue is that when creating scheduled mailings based on smart groups, the recipients are calculated when a scheduled mailing is created and not updated at time of sending. This causes issues because emails don't go to whom they are expected to. This prevents people from being able to use the scheduled mail feature normally; my clients may make test emails in advance, but they have to go in manually and update the recipients before sending out each mailing.

I've heard that part of the issue with resolving this comes down to ACLs.

I'm a Joomla user. I don't know if it is different for other CMSes, but I run a cron job to process my scheduled jobs every 5 minutes (following whatever schedule civi has). For that to execute, I have to pass in a user and password. Now, I know that is a Joomla user, but that user has to have proper CiviCRM permissions. If this is similar for other CMSes, I would think you would just update the recipients based on that cron job user's permissions.