Postmaster is a simple (and craptasticly coded) addon that automates mass mailing to members of your guild. Here's step-by-step instructions:

1. Open your mailbox
2. Go to the "Send Mail" tab
3. Write in a subject and the body (no sender)
4. Execute /postmaster <guild rank>[+?]
5. Wait for it to finish (you can't do -anything else- while it's mailing)

The syntax for the slash command is simple; <guild rank> is for example "Member", "Class Leader", and similar (without the quotes). If you end the command with a '+' sign, that means anyone with that rank AND ABOVE will get the mail.

So in a typical guild structure, you have some form of the following: Guild Master, Officer, Class Leader, Member, Initiate

If you were to type /postmaster Class Leader+, for example, all Class Leaders, Officers and GMs would get the mail. If you type Initiate+, EVERYONE will get it. If you just type /postmaster Class Leader (without +), ONLY Class Leaders will get the mail.