In a seeming attempt to undercut the competition, the U.S. Postal Service is putting into effect new rules that have private mailbox rental firms irate.

• Many small companies that use the addresses of private mailing service stores like to tack on the word "suite" or other number to the store's street address without mentioning the store's name -- which they feel gives customers the impression they operate in a big office building.

• But the USPS has begun requiring such mail to include the designation PMB -- for private mailbox -- in the address, and says it will not deliver mail without the designation after six months.

• Another new rule prohibits the stores from returning to senders postage-free -- as has been customary -- first- class mail addressed to former customers who have moved.

• The stores will have to forward that mail to former customers with new first-class postage attached.

The postal service first proposed the new rules in 1997 and received more than 8,000 complaints.

USPS began offering packing services on a trial basis in 1994, in direct competition with the private firms. But their charges were too high and the experiment was abandoned.

There are more than one million private rental mailboxes in the nation and 10,600 pack-and-send stores.

Source: Rodney Ho, "Post-Office Rule Incenses Renters of Private Boxes," Wall Street Journal, May 3, 1999.