This has got to be one of my favorite projects I ever made, it went through four very important stages before now, I haven't done anything on this recently, and it's fairly complicated. Using only 1 named brick per email client, and one named brick for the MPU.
Lets start with what I will call the MPU, mail processing unit, why do I call it that? I call it the MPU because it choses where to send the mail! Cool right?
Next we are onto clients, there are 2 buttons and message slots, red clears the messages, green lets you send messages, first it asks you Team chat or Regular chat, you will answer with a prompt, Next you say the box you want to send to, for example, if I were to send to lets say myself, I would say Ben's box, or something similar. then you click the green button again and it asks you to put in your message, put in your message for example lol and click the green button, congratulations message sent to Ben's box, the message being lol.
So what you might ask? well, this lets you send a message and it will be saved in that spot, even if the person is not in the server! Say your friend doesn't get to go on Blockland today, but you are leaving for vacation and your dedicated server is in his hands until you get back, leave him a message in his house's box and when he goes in he can see what you sent him!
Now for pictures explaining what this looks like, and how it is used, oh and sorry it is kind of ugly, not a great builder :/
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This is the first image you will be presented with, choosing team chat or regular chat.

This is the second image, after you pick who you want to send to.

This is the final image, Congratulations I received the message!
SAVE
http://www.4shared.com/file/xiQKm_OT/Benofdooms_email.htmlTo add more boxes, dupe the boxes, and change the named brick, the one above the row on the very left, or in my boxes case, the letter B.
Then add two events to the glowing circle in a glass box, they are already there, but be sure to set the right named brick!