class mailbox :?name:string -> string list -> addr_spec ->object..end
mailbox has a name, optionally a route (not used nowadays), and
a formal address specification.
Create a mailbox with
new mailbox ~name route addr_spec
Pass route = [] if not used (formerly, routes were used to specify
the way the mail should take from the sender to the receiver, and
contained a list of hostnames/IP addresses).
method name : stringNot_found if not setmethod route : string listmethod spec : addr_spec