It happens quite often that people send "flowed" messages, but failed to
declare them properly (I'll attach such a message - I hope Emacs will
not strip the SPCs at the end of the lines).  Run `W w' on such a
message will fill it nicely, but it will not determine paragraphs ends
properly (after "Preface", after "worldwide access.", etc.).  Lines to
be flowed together end with a SPC, paragraph ends end with a non-SPC
character.

I'd like to propose to make the washing function add an additional at
the end of an paragraph.