> This is very similar to VERP, which encodes the recipient's address in
> the SMTP envelope return path. The advantage of VERP is that it can be
> used for each delivery--obviating the need for special probes, and
> allowing the list manager to keep track of which messages have bounced
> to which subscribers.
The disadvantage of doing this every time for every recipient is that
it means that a separate copy of the message must be sent for each
recipient. While this isn't a big problem for a typical list with
recipients scattered over many hosts (as long as the list server can
get the copies into the SMTP server's queue fast enough), it is a
problem in a situation where there are hundreds or thousands of
recipients on one host.
