Syntax:
SET HIDE {EMAIL | USERMASK | QUIT} {ON | OFF}

Allows you to prevent certain pieces of information from being displayed when someone does a NickServ INFO on your nickname. You can hide your E-mail address (EMAIL), last seen user@host mask (USERMASK), and last quit message (QUIT). The second parameter specifies whether the information should be displayed (OFF) or hidden (ON).

E-mail addresses are automatically hidden from the public unless you choose to display it with the SET HIDE command.