That can be a little tricky... Outlook gurads that list to ensure that
virus's don't use it. Depending on what version you are on this might work
for you...

Option Explicit
Const CdoPR_EMS_AB_PROXY_ADDRESSES = &H800F101E
Const g_strMAPILogOn                As String = "MS Exchange Settings"
Const g_strAddressList              As String = "Global Address List"
Const g_strEMailAddressIdentifier   As String = "SMTP"

Sub Test()

   MsgBox GetEMailAddress("James Thomlinson")

End Sub

Public Function GetEMailAddress(ByVal strName As String) As String
   Dim objSession          As MAPI.Session
   Dim objField            As MAPI.Field
   Dim MyAddressList       As MAPI.AddressList
   Dim MyAddressEntries    As MAPI.AddressEntries
   Dim MyEntry             As MAPI.AddressEntry
   Dim SomeEntry           As MAPI.AddressEntry
   Dim MyRecipient         As MAPI.Recipient
   Dim v   As Variant
   Dim strReturnValue As String
   
   'Initialize Local Variables
   strReturnValue = "No Address Found" 'Retrun Value if not found
   
   ' Create Session object and Logon.
   Set objSession = CreateObject("MAPI.Session")
   objSession.Logon (g_strMAPILogOn)
   
   'Create the Address list from the Global Address List
   Set MyAddressList = objSession.AddressLists(g_strAddressList)
   If MyAddressList Is Nothing Then
       MsgBox g_strAddressList & " Unavailable!", vbCritical, "Critical
Error"
       Exit Function
   End If

   'Initialize MyAddressEntires with the entries in the Address List
   Set MyAddressEntries = MyAddressList.AddressEntries
   
   'Traverse through the entries searching for a match
   For Each SomeEntry In MyAddressEntries
       Set MyEntry = SomeEntry
       If Trim(UCase(strName)) = Trim(UCase(MyEntry.Name)) Then
           Set objField = MyEntry.Fields(CdoPR_EMS_AB_PROXY_ADDRESSES)
   
           ' PR_EMS_AB_PROXY_ADDRESSES is a multivalued property
(PT_MV_TSTRING).
           ' Therefore, you need to extract the individual members.
           For Each v In objField.Value
               If InStr(1, UCase(v), g_strEMailAddressIdentifier) Then
                   strReturnValue = Mid(v, 6, 256)
                   Exit For
               End If
           Next    'Next Field Value
       Exit For
       End If
   Next    'Next Address Entry
   
   'Return Function Value
   GetEMailAddress = strReturnValue
   
   'Housekeeping
   Set objField = Nothing
   Set MyAddressList = Nothing
   Set MyAddressEntries = Nothing
   Set MyEntry = Nothing
   Set MyRecipient = Nothing
   objSession.Logoff
   Set objSession = Nothing
   
End Function

You need to reference the Microsoft CDO 1.2? (Part of the install for
outlook) library to use this code. It takes a person's name and returns their
E-mail address from the global address list...