1. It is possible to tell the username, at which domain it belongs, and often whether or not it was a forwarded mail, and through whom it has been forwarded.
2. CC: is used if you want to send a copy of the message to someone else apart from the recipient. Useful for notifying a connected thrid party that a communication has been made between two people. BCC: Is same as CC except adds the function that the recipient is not made aware of the copy sent out. Reply All is useful in order to send a reply to every person on the recieving list of a message you've recieved, such as in in group communications, ie clubs, friends. Can be a dangerous function!
3. Use easily opened file types eg .txt, .jpg. Make files smaller, eg. convert .bmp to .jpg. Zip or RAR large files or large numbers of files (another from of compression), but be aware that file types must be opened by the end user, so inform them that the will need WIn RAR if you have sent a .Rar or Acrobat if you have sent a .Pdf for example.
4. I have my email account set to exclusive, so only emails that have addresses saved into my address book or safe list are put into my email inbox. This filter out Junk Mail, but requires, however, that I check my Junk Email (where everything else goes) occasionally to make sure that people are not sending me things that I do want to recieve but from unrecognised accounts. I then add them to my contacts or safe list to avoid future slip ups (Junk Mail is deleted every ten days).
5. My folder structure is organised into inbox, junk mail, comedy, writing.
Most emails remain in my inbox, organised by date, where i can search for mails by keywords and usernames. Comic emails are transferred into Comedy folder, so there is a stock of comedy for future reference. Writing is saved for emails relating to my business, writing childrens books. Junk mail is used as per answer 4.