This is readonly property that is used to get reference
(to access) of some message from collection of all messages
for the user. Once you add new
message to the collection (either using Filename parameter
or without it), new Pop3Message object
will be created and all information regarding that message
will be stored there. You can access message's
properties and change those values at will, although you
shouldn't do it after user starts reading messages
because it may confuse the client.
Usually Item keyword can be left out from command
because it's default (enumerator) property.
Please note that, unlike other collections in VB,
indexes start from 0 and go up to Count-1. So,
first user has Index=0.