I forgot to post the fully revised code so here it is:

[VBA]
Sub badAddress()
Dim olApp As Outlook.Application
Dim olNS As Outlook.NameSpace
Dim olFolder As Outlook.MAPIFolder
Dim regEx As Object
Dim olMatches As Object
Dim strBody As String
Dim bcount As String
Dim lFirstPos As Long
Dim lLastPos As Long
Dim badAddresses As Variant
Dim i As Long
Dim xlApp As Object 'Excel.Application
Dim xlwkbk As Object 'Excel.Workbook
Dim xlwksht As Object 'Excel.Worksheet
Dim xlRng As Object 'Excel.Range

Set olApp = Outlook.Application

Set olNS = olApp.GetNamespace("MAPI")
Set olFolder = olNS.Folders("Archived E-Mail").Folders("Inbox").Folders("Mail Failures")
Set regEx = CreateObject("VBScript.RegExp")

'define regular expression
regEx.Pattern = "[\_]*([a-z0-9]+(\.|\_*)?)+@([a-z][a-z0-9\-]+(\.|\-*\.))+[a-z]{2,6}"
regEx.IgnoreCase = True
regEx.Multiline = True

' set up size of variant
bcount = olFolder.Items.Count
ReDim badAddresses(1 To bcount) As String

' initialize variant position counter
i = 0

' parse each message in the folder holding the bounced emails
For Each Item In olFolder.Items
i = i + 1
strBody = Item.Body
Set olMatches = regEx.Execute(strBody)
If olMatches.Count >= 1 Then
badAddresses(i) = olMatches(0)
Item.UnRead = False
End If
Next

' write everything to Excel
Set xlApp = GetExcelApp
If xlApp Is Nothing Then GoTo ExitProc

Set xlwkbk = xlApp.Workbooks.Open("My Folder Path Goes Here.")
Set xlwksht = xlwkbk.Sheets(1)
Set xlRng = xlwksht.Range("A1")

xlApp.ScreenUpdating = False
xlRng.Value = "Bounced email addresses"

' resize version
xlRng.Offset(1, 0).Resize(UBound(badAddresses) + 1).Value = xlApp.Transpose(badAddresses)
xlApp.Visible = True
xlApp.ScreenUpdating = True

ExitProc:
Set xlRng = Nothing
Set xlwksht = Nothing
Set xlwkbk = Nothing
Set xlApp = Nothing
Set olFolder = Nothing
Set olNS = Nothing
Set olApp = Nothing
Set badAddresses = Nothing
End Sub

Function GetExcelApp() As Object
' always create new instance
On Error Resume Next
Set GetExcelApp = CreateObject("Excel.Application")
On Error GoTo 0
End Function
[/VBA]