Thank you so much for your advice, Bob. I felt responding to the 2nd notice with a copy of first response was the best alternative but I needed reassurance. I can't even find any notice CP5048 in the IRS offerings! The first response was sent certified but the extension was sent by regular mail which has been my routine for the past 20 years with this particular corporation without a problem. I just hope the IRS understands what we preparers have been going through.