the US mail will be severly slowed or stop all together
Who still uses the U.S. Mail?
Correspondence is faxed or emailed, packages go commercial. Only thing I get via U.S. Mail is bills and Class IV junk, none of which could be labeled "suspicious" and all of which are easily recognizable.
your answer is in your post...you receive bills...you also use the mail system to send out payments. If the mail service is stopped, companies will not get thier funds.