Separate thousands of emails into 1000 group.

Do you want them to be sequential from the list or do you just want a random 1000? A macro is the way to go here.

Option Explicit

Sub Thousands()
    Application.ScreenUpdating = False
    Dim lr As Long, x As Long
    Dim ws As Worksheet
    Set ws = Sheets("Sheet1")
    'assumes emails are in column A.  Find the last row
    lr = ws.Range("A" & Rows.Count).End(xlUp).Row
    x = Int(lr / 1000) + 1
    Dim j As Long
    Dim Last As Long
    Dim sname As String
    sname = "Email"
    Last = x
    For j = 1 To Last
        Sheets.Add After:=Sheets(Sheets.Count)
        Sheets(Sheets.Count).Name = sname & j
    Next j
    Dim i As Long
    j = 1
    For i = 1 To lr
        ws.Range("A" & i & ":A" & i + 999).Copy
        Sheets(sname & j).Range("A1").PasteSpecial xlPasteValues
        j = j + 1
        i = i + 999
    Next i
    Application.CutCopyMode = False
    Application.ScreenUpdating = True
    MsgBox "complete"
End Sub

If that takes care of your original question, please select Thread Tools from the menu link above and mark this thread as SOLVED. Thanks for the rep!