I am trying to fetch all the user email addresses from outlook.
In the sheet I have a list of names of the user.

VBA macro version for Excel to read names from column D, search the Outlook Address Book (GAL and Contacts), and fill email addresses in column E. This uses late binding—no need to set VBA references.
what is late binding when it comes to vba and outlook?

does it really matter?

Sub LookupOutlookEmails()
    Dim olApp As Object
    Dim olNS As Object
    Dim olRecipient As Object
    Dim olExUser As Object
    Dim ws As Worksheet
    Dim lastRow As Long
    Dim i As Long
    Dim name As String
    Dim email As String

    ' Use the active worksheet
    Set ws = ActiveSheet
    lastRow = ws.Cells(ws.Rows.Count, "D").End(xlUp).Row

    ' Connect to Outlook
    On Error Resume Next
    Set olApp = GetObject(, "Outlook.Application")
    If olApp Is Nothing Then
        Set olApp = CreateObject("Outlook.Application")
    End If
    On Error GoTo 0
    If olApp Is Nothing Then
        MsgBox "Outlook is not running or not installed.", vbCritical
        Exit Sub
    End If
    Set olNS = olApp.GetNamespace("MAPI")

    Application.ScreenUpdating = False

    For i = 2 To lastRow
        name = Trim(ws.Cells(i, "D").Value)
        email = ""
        If Len(name) > 0 Then
            Set olRecipient = olNS.CreateRecipient(name)
            olRecipient.Resolve
            If olRecipient.Resolved Then
                On Error Resume Next
                Set olExUser = olRecipient.AddressEntry.GetExchangeUser
                If Not olExUser Is Nothing Then
                    email = olExUser.PrimarySmtpAddress
                Else
                    ' Use Address property for contacts (may return Exchange X500 if not SMTP)
                    email = olRecipient.AddressEntry.Address
                End If
                On Error GoTo 0
            Else
                email = "NOT FOUND"
            End If
        End If
        ws.Cells(i, "E").Value = email
    Next i

    Application.ScreenUpdating = True
    MsgBox "Email lookup complete!", vbInformation
End Sub