When emailing, I often need to reference information from messages either sent or received, and currently gmail requires me to save a draft of the message I’m writing, and then search for the email I need to reference and then open the draft again, and there is no way I know of to toggle between one or two or more messages easily, so sometimes I have to save a draft again and repeat this process a couple times. An easy fix for this would be to have tabs, so I can easily search for and select emails I need to reference, and toggle between different emails, while writing an email.
[update: it’s been ages since I’ve used Outlook - doesn’t it have this ability? Yahoo Mail does.]