[cobalt-users] POP3 Scanning

["VFastlink Support Team" <support@xxxxxxxxxxxxx>]

  Recently we have seen an increase in POP3 scanning.  The robot will open a
POP3 connection and try to login as some user.  When the server says, "No
such user here", it continues until it finds a valid email account.  I call
this trolling for valid mailboxes.  I'm sure there is a more techie term for
it.

Anyway, has anyone found a good, solid way to prevent these people from
doing this?  Even if we could prevent the "No such user" response for
invalid mailboxes, it would at least render their activities as useless.