Help for DELETE:

DELETE allows you to delete memos from your
inbox. You can either delete all memos with
the all parameter, or specify a memo number.
You can obtain a memo number by using the LIST
command.

You can also SEND, READ, LIST and FORWARD memos.

Syntax: DELETE all|<memo number>

Examples:
    /msg &nick& DELETE all
    /msg &nick& DELETE 1