In message e.net, at
10:30:06 on Wed, 20 Sep 2006, Mark Goodge
remarked:
Take a look at any commerciallly posted letter that
you've received lately, and wonder how Royal Mail manage to avoid the
franking mark being used repeatedly. But, because it's a long-standing
problem, it has a number of long-standing solutions.

The main element of the solution at the sending end was that the
franking machine only produced one "stamp" for each transaction. If you
messed it up (for example, franked the print roller rather than a
letter, it was just tough luck.
--
Roland Perry