[no subject]

You are moving from dovecot to MS Exchange?
IIRC Exchange does not bother to accept mails with this flag and will 
more or less silently not transfer the marked mail.

FWIW, I migrated from cyrus to Exchange using the following command 
line:
/root/bin/imapsync.1_278 \
 --host1 $CYRUSSERVER --user1 $CYRUSUSER \
 --authuser1 cyrusadmin --password1  PWCHANGED \
 --host2 $EXCHANGESERVER --user2 $EXCHANGEUSER \
 --authuser2 exchangemigration --password2  PWCHANGED \
 --useheader 'Message-Id' --useheader 'Message-ID' \
 --useheader 'Received' \
 --nofoldersizes \
 --skipsize \
 --regexflag 's/(\A[^\\]\w+\s)|(\s[^\\]\w+)//g' \
 --regexflag 's/(\$No.Junk)//g' \
 --regexflag 's/(No.Junk)//g' \
 --regexflag 's/(Seen-handled)/Seen/g' \
 --regexflag 's/(Junk)//g' \
 --regexflag 's/(\$)//g' \
 --regexmess 's/^Message-Id/Message-ID/i' \
 --regextrans2 's/.Drafts{,1}$/Drafts/' \
 --regextrans2 's/^INBOX$//' \
 --regextrans2 's/(.{1,})/\/$1/' \
 --regextrans2 's/(.*)/INBOX$1/' \
 --regextrans2 's/\.Draft[s]{0,1}$/Drafts/' \
 --regextrans2 's/.*\/Drafts/Drafts/' \
 --regextrans2 's/.*\/.Sent/Sent\ Items/' \
 --exclude '.Trash$' \
 --fastio1 --fastio2

So I had a big deal with removing flags Exchange does want to know about 
and moving folders to places where an Exchange user expects her/his 
mails.

I looped it for 2 weeks in 4 threads over all users with a final run 
after the deliver switch.
I do not recall any issues with deleted mails, except omitting the 
.Trash folder from squirrelmail or TB.

There were warnings and sometimes not transferred mail boxes due to 
other flags I did not cover here, but that affected only about 10 out of 
approx 2000 mailboxes.
As written in an other thread here, if there were messages not 
transferred due to "Keywords are not supported", these messages were 
successfully transferred during the next loop.

Greetings,

Stefan
-- 
Stefan Schmidt zu Hause
Bremen