Check if a pop3 email account exists in a windows 2003 pop3 service 

...
  Dim exists
  exists = ExistsPop3User("hlavni", "franta", "market.cz")
  exists = ExistsPop3Email("hlavni", "franta@market.cz")
...


'Checks If a user account exists In a Windows 2003 POP3 service
'2005 Antonin Foller, http://tips.motobit.com
Public Function ExistsPop3User(MachineName As String, _
  UserName As String, DomainName As String)

  'get a configuration object.
  Dim P3 As New P3ADMINLib.P3Config
  'get the object from a VB Script/JScript
  'Set P3 = CreateObject("P3Admin.P3Config")
  'Connect To the remote computer.
  If Len(MachineName) > 0 Then P3.MachineName = MachineName
  
  Dim Domain As P3ADMINLib.P3Domain
  Dim User As P3ADMINLib.P3User
  
  'get the domain object
  Set Domain = P3.Domains.Item(DomainName)
  
  'add a user account
  On Error Resume Next
  'get the created user account
  Set User = Domain.Users.Item(UserName)
  ExistsPop3User = Err = 0
End Function

Public Function ExistsPop3Email(MachineName As String, Email As String)
  Dim vHelp() As String
  vHelp = Split(Email, "@")
  ExistsPop3Email = ExistsPop3User(MachineName, vHelp(0), vHelp(1))
End Function

<A
 Href="http://www.motobit.com/tips/detpg_check-pop3-user-account-windows/"
 Title="Let's you check if a pop3
  user email account exists in
  a windows 2003 pop3 service"
>Check if a pop3 email account exists in a windows 2003 pop3 service</A>