One feature that would be very useful to be added to usermin is the ability to be able to create an email and schedule it to be sent at a later time/s. On the Compose Email screen could be a new tab called Schedule with an option for Now (which would be the normal) or you could select date and times for the email to be sent. A new folder called scheduled could be created to keep all the scheduled emails in. Then at the scheduled date and time the server could send the email out for you and place a copy in the sent folder.
There is a similar feature as an add on in thunderbird called Sendlater. While this is useful it would be better to have this feature on the server because the server is running all the time. Also in Thunderbird this feature only allows you to schedule an email to be sent once and if your computer is off at the scheduled time the email does not send at all.
This does sound like a pretty nifty idea, though I’d want to see it as an optional feature, possibly a module, rather than something that is always visible (just like it’s an add-on in Thunderbird). Complexifying the default UI for special cases is pretty much no longer allowed in any of the *mins (gods know we have enough complexification for special cases sitting around in the UI from before this policy existed), and this is definitely a special case. I have wanted to schedule an email maybe twice in the 24 years I’ve been using email, though I suspect for the people that want it, they have reasons to use it much more often.
It would be relatively easy to build, I think, since Usermin already has at and cron jobs modules, so it’s trivial to add new scheduled jobs via the API. I’m not sure if regular modules can have plugins though (Virtualmin can, but it has hooks specifically for the purpose). It’d be easy to make a menu item, though, for “Compose an email to send later” or something like that, and have it open a compose form. It would just use the Read Mail module API for doing the work. There’s probably even an API call for the compose window, but, I might be wrong about that. This does have the negative that you couldn’t click “Send Later” after composing the message, though.
Maybe the scheduler needs to be turned on and off from the Mail Preferences, Date and Time Settings screen. But surely when the schedule feature is turned on the most logical thing is to use the current UI rather than writing a whole new one for what is essentially just a feature of sending emails. Maybe we are talking about the same thing.
I understand what you are saying about complicating the UI but to my mind there are some things that inherently belong in the UI (when on) and this is one of them.