Then supply them with a fee that includes your overnight fee charged from  your company to theirs.  Any overnight service can give you this fee by giving them both addresses.  Federal express now has a new three-day saver plan.  Most companies give you 5 days for return of certified copies.  However, I send all my packages to SC by Priority Mail/Flat Rate (post office) which is received within 2 days.  They do want you to use the confirmation addition though - it is traceable by accessing the United States Postal service site online and entering the number - the slips are right by the certified mail slips at the post office.  I buy laser printer labels and print out sheets to the companys' addresses so I have them readily available to slap on a package in a rush.  Of course this is why I charge more than the actual postage too - it does cost.