The SMTP root directory is root:\Inetpub\Mailroot.
Within the root directory are four folders:

• Drop Stores incoming messages from all domains hosted on the computer. You can assign any directory to be the Drop directory, except one that has already been designated as the Pickup directory. This feature is not available on an Exchange 2000-based server.
• Pickup Processes outgoing messages that are created as text files and copied to the directory. When a properly formatted RFC 822 message is copied to the Pickup directory, the SMTP service collects it and initiates delivery.
• Queue Holds messages waiting for delivery when they cannot be delivered because the connection is busy or down.
• BadMail Stores undeliverable messages that cannot be returned to sender.