1. Mailbox quota (the admin configures this). Users like to send attachments and leave them in the mailbox, using up resources. By having quota it forces them to clean out the mailbox. (Received/Sent/Deleted all part of the quota)

2. Message status of sent messages (unread, read (including time read), and deleted). Users want to know if the recipient got the email.

3. Unsend email (that is unread by recipient).

4. One more tab showing deleted messages with a way to undelete if user deletes by mistake.

Are there any plans to do this in the future?