@Derek Curtis - sorry for the late reply. For some reason this discussion dropped out of my favorites list.
What I'm referring to is the ability for the list creator (list admin, list owner, whatever you want to call them) to control WHO can unsubscribe from a list.
In Exchange, a distribution list can be created to allow members to self-unsubscribe AND there is the option that only a list administrator can add/delete users, which is perfect for guaranteeing an employee cannot unsubscribe themselves from essential corporate communications.
The problem is that in Smartermail, there is no list option to "include all domain users". That option is only available to aliases. So, the client had to create an email alias and turn ON the switch labeled "Include all domain users".
Then they added that alias as the subscriber to a mailing list. Here's the problem.... because the list sent to a SINGLE recipient (the alias) if ANY domain user hit the Unsubscribe link in webmail (or in their email client if offered), it would unsubscribe the alias itself. So the next time a blast was sent to the mailing list, instead of 1800 users receiving an email from the CEO, nobody would get it because the alias that included all users had been removed by a single user hitting the Unsubscribe link.
Why use an alias as the sole recipient in this case? Because-- 1800 users. Having to MANUALLY maintain that many users, in a company that saw dozens of new-hires and terminations monthly, would have been a huge waste of resources. And since it would be a manual process, prone to accidental omissions. Using the "all domain users" enabled alias was the perfect solution for the list always including everyone.... until some knucklehead hit Unsubscribe.
Other question, Why use a list instead of just emailing the alias directly? Because their leadership wanted all list messages to show the name of the list as the sender.
Short answer is: Give list admins/owners the OPTION of disallowing users from self-unsubscribing, like Exchange already does.