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.