I ended up finding a way to make it work by making a frankencode using some lines from someone who had another problem related to SelectNamesDialog.Display. I am fully aware that the resulting code is very ugly. If someone is kind enough to help me make it pretty, or to explain to me the logical difference between what i originally did ad this code, i would be thrilled.
Private Sub ListeAdresse_Click()
Dim EmailAddress As String
Dim myAddrEntry As AddressEntry
Dim exchUser As Outlook.ExchangeUser
Dim oDialog As SelectNamesDialog
Set oDialog = Application.Session.GetSelectNamesDialog
With oDialog
.InitialAddressList = Application.Session.GetGlobalAddressList
.ShowOnlyInitialAddressList = True
If .Display Then
AliasName = oDialog.Recipients.Item(1).Name
Set myAddrEntry = Application.Session.GetGlobalAddressList.AddressEntries(AliasName)
Set exchUser = myAddrEntry.GetExchangeUser
If Not exchUser Is Nothing Then
EmailAddress = exchUser.PrimarySmtpAddress
End If
CourrielSup.Caption = EmailAddress
End If
End With
Set olApp = Nothing
Set oDialog = Nothing
Set oGAL = Nothing
Set myAddrEntry = Nothing
Set exchUser = Nothing
End Sub