The Post Office does not do well with handwritten addresses.  I always send an envelope with computer-printed return address, when I send a bill.  And if I ask a client to mail me anything else, they will get an addressed envelope.  

The highest levels of PO management are embroiled in political scandal and budget restraints.  The troops are generally doing the best they can.  Keep track of average delivery time for mail you receive, and if it is consistently not meeting standards, file a complaint online.  It will get down to your local postmaster, while drawing attention at higher levels.  I did that for a package (not business-related) that was lost for a couple months -- the postal worker who investigated it called to apologize when they couldn't find it, and then called again to apologize when it eventually turned up.