MemoServ

MemoServ is a utility allowing IRC users to send short messages to other IRC users, whether they are online at the time or not, or to channels(*). Both the sender's nickname and the target nickname or channel must be registered in order to send a memo.

(*) By default, any user with at least level 10 access on a channel can read that channel's memos. This can be changed with the ChanServ LEVELS command.