On form load make sure you set properties: (Also can be done in the properties window)
Code:
Me.txtEmailUser.AutoCompleteSource = AutoCompleteSource.CustomSource
Me.txtEmailUser.AutoCompleteMode = AutoCompleteMode.Suggest
For example when adding a new entry.
vb Code:
Private Sub btnAddNewSuggest_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAddNewSuggest.Click
If String.IsNullOrEmpty(Me.txtAddToList.Text) Then
Exit Sub
End If
Me.ListBox1.Items.Add(Me.txtAddToList.Text)
Me.txtAddToList.Clear()
Me.SetCompleteList(Me.txtEmailUser, Me.ListBox1.Items)
End Sub