a joke, say, or a survey - since this happens all the time, and since everyone seems to kill the formatting when doing it, getting it all on one line (does no one notice this or does no one care?)...
maybe slow down (Yeah. RIGHT. sure...) and try this before you stash...
take whatever you're copying from the mailing-list- take the leading > at the beginning of the line...
replace it (use search-replace in a good text-editor, probably not in Microsoft Word, but there are some good programs for this that are free)
with <br />
(do a change all)
you'll get some real- not accidental leading > - converted to breaklines by accident, so take a moment to check that you didn't change the meaning of the text by what you just did, but aside from that, do a copy-replace now and stash it.