After Christopher Lindsey's response, Bill Houle followed up:
| If I feed the mbox intact, the first From_ is fixed and the rest are
| escaped. (If I use -b, then all From_ lines are unchanged.)
| If I remove all the From_s, the first message is fixed but the others are
| treated as part of the first message body and never From_ized.
Two indications that formail isn't splitting.
| To reiterate, I know formail fixes the From_. The splitting is the tricky
| part. If I had all 589 messages each in their own file, then formail on
| each would work like a charm.
Bill, have you tried formail -es? Without -e, formail will look for embedded
postmarks only immediately after each blank line. -e makes it check each
line; it's slower but sometimes you need it. I get the feeling that that
might be the case here. I know from personal experience that @-style
addresses in postmarks don't upset formail -s in the least, any more than
local addresses that have neither bangs nor ats nor dots.
You might also use -Yes (or -yes) to make formail ignore Content-Length:
headers.