Mail is the primary communication tool of the Internet so it seems logical that WoW would feature its own mail system. Also, in case you were wondering, the WoW mail system is in-game only, you cannot send mail to standard email addresses.
How do I send Mail?
Throughout the game world there are mailboxes where players can collect their mail sent to them by other players. The mailboxes are in towns and around key areas such as Inns and Banks. You have to collect your mail from a mailbox by visiting one, there is no other way to check your mail.
So why would you use mail? Mail in WoW is useful for numerous reasons besides being a way to communicate with your friends who may be offline. Not only can you send messages but you can also attach items to any mail you send. You can even mail items and cash to other characters on your account, provided they are on the same faction and same server.
There are 3 types of mail you can send in WoW:
Normal Mail : This contains a message and the recipient receives it instantly in his mailbox. This mail lasts for 30 days before it is automatically deleted.
Package : In addition to a message, you can attach an item to your mail. The recipient will receive the item in his mail after one hour of sending it. This mail (along with the item) also lasts for 30 days before it is bounced back to the sender.
Underneath the main message box there is a slot for an attachment . Open up your inventory and drag the item into the slot. This is useful for sending items from one of your characters to another (within the same faction and server).
If you do not type a subject for your email the system will automatically enter the item name as yoru email subject.
You can also send currency via the mail system by adding in the amount you wish to send into the currency denomination boxes.
Cash on Delivery (CoD) : In addition to a Package mail, you may wish to receive cash in return for the item. Select the C.O.D ( Cash on Delivery ) option, enter the amount in gold, silver and copper and then the recipient of the mail will need to pay you that amount before they can get the item you've attached. Ideal for completing trades . The transfer of money is done automatically by mailing the cash back to the sender. CoD mails will last for 3 days and if it has not been opened, it'll be returned to sender.
It costs 30 copper pieces to send any mail, regardless if there is an attachment or not, however if you set it to C.O.D., the recipient pays it (if they accept your mail). You can't keep copies of mails that you've sent and you can't forward a mail you've received from one person to another, but you can keep copies of mails you have received in your inventory as the game will create an letter containing the text of the mail for you if you want such an item.
There are some rules with sending mail though. You must type a Subject and the target player to send to must exist. You cannot mail conjured items, quest items or soulbound items. You cannot mail someone who has placed you on their ignore list. And finally, there IS a limit to the amount of mail you can receive in your inbox before the excess gets bounced back.