Set all the appropriate ExportOptions and then call the Export method.

Code:
If blnPreview = True Then
   Set frmCrystalViewer.mRptReport = SalesInvReport
   frmCrystalViewer.Caption = strTitle & "Invoice"
   frmCrystalViewer.Show 1
Else
   SalesInvReport.ExportOptions.DestinationType= crEDTMicrosoftExchange
   SalesInvReport.ExportOptions.MailToList = "....
   SalesInvReport.Export
End If