Get current user - signed to exchange server - manager email address

How can I retrieve the current user manager email address? I'm only able to get my e-mail address by calling the

Application.Session.CurrentUser.AddressEntry.GetExchangeUser

while using

Application.Session.CurrentUser.AddressEntry.GetExchangeUser.Manager

returns nothing... What i'm trying to achieve is to send an email to my manager right from excel sheet and automate it on other users computers (because they've other managers)

Sub Mail_workbook_Outlook_1()
    Dim OutApp As Object
    Dim OutMail As Object

    Set OutApp = CreateObject("Outlook.Application")
    Set OutMail = OutApp.CreateItem(0)

    If IsEmpty(Range("A21").Value) = True Then ' check if cell is empty
      MsgBox "Cell is empty!", vbCritical, "It would be better to not left it empty..." ' if so, show user a message
    Else

    On Error Resume Next
    With OutMail ' outlook message details
        .To = "xyz@xyz.net"
        .Subject = "Sales report - " & Format(Date, "dd-mm-yyyy")
        .Body = "Here comes the full sales report from " & Format(Date, "dd-mm-yyyy") & Application.Session.CurrentUser.AddressEntry.GetExchangeUser
        .Attachments.Add ActiveWorkbook.FullName ' add current file as an attachment to the outlook message
        .Send
    End With
    On Error GoTo 0
    MsgBox "File sent ", vbInformation, "You can now safely close the report" ' show confirmation message

    Set OutMail = Nothing
    Set OutApp = Nothing
    End If
End Sub

To get current User's Manager.

Example on outlook-vba

Option Explicit
Sub GetManager()

    MsgBox CreateObject("Outlook.Application").GetNamespace("MAPI") _
                    .CurrentUser.AddressEntry.GetExchangeUser.Manager

End Sub

Edit

Remember user must have manager setup.

Modify your code this way

    With OutMail ' outlook message details
        .To = CreateObject("Outlook.Application").GetNamespace("MAPI") _
                    .CurrentUser.AddressEntry.GetExchangeUser.Manager

        .Subject = "Sales report - " & Format(Date, "dd-mm-yyyy")
        .Body = "Here comes the full sales report from " & Format(Date, "dd-mm-yyyy")
        .Attachments.Add ActiveWorkbook.FullName 'attachment File 
        .Display
'        .Send
    End With

Also See on MSDN Example

How to: Get Availability Information for an Exchange User's Manager