>> Is it becoming common practice to sliently drop messages instead of
>> bouncing them (because of forged return-paths) ?
>
> Yes. If you send a bounce message for unknown recipients, you get
> used for backscatter attacks
This is not true for *rejections*, rather than bounces. Rejection is the
appropriate response to spam and forgery.
However, as organisations outsource their spam filtering, testing for
valid addresses etc. becomes difficult. For this reason and others, many
spamfilter outsourcing companies now tend to discard silently, even in
situations where they could have rejected the mail properly.
Vic.