Transferring to/from Gmail accounts to a Google Apps account with imapsync. Also good for GApps to GApps transfers, archives, or migrations.

sync_mail.sh

#/!/bin/bash
# Most of the tweaks here are wrapped up in gmailmig
#    https://code.google.com/p/gmailmig/
#
# Props to brave folks who figured this out before me
#    http://imapsync.lamiral.info/FAQ
#    http://www.thamtech.com/blog/2008/03/29/gmail-to-google-apps-email-migration
#    http://seagrief.co.uk/2010/12/moving-to-google-apps-with-imapsync/
#    http://blog.mcfang.com/tag/imapsync/
#
# Loop thorugh multiple times as things behave better working in 500mb chunks (-exitwhenover 500000000)
#    http://mywiki.wooledge.org/ProcessManagement#OK.2C_I_have_its_PID.__How_do_I_check_that_it.27s_still_running.3F

# Going from OLDGMAIL@GMAIL.COM to NEWGMAIL@GAPPS.COM
for i in {1..10}
do
  ./imapsync  –split1 100 –split2 100 --fast --syncinternaldates --nocheckmessageexists --allowsizemismatch --exitwhenover 500000000 -host1 imap.gmail.com -host2 imap.gmail.com -port1 993 -port2 993 --ssl2 --ssl1 --authmech2 LOGIN --authmech2 LOGIN \
  --pidfile '/tmp/imapsync.pid'
  -user1 OLDGMAIL@GMAIL.COM -password1 OLDGMAILPASSWORD \
  -user2 NEWGMAIL@GAPPS.COM -password2 NEWGAPPSPASSWORD \
  --regexmess 's/Delivered-To: OLDGMAIL\@GMAIL.COM/Delivered-To: NEWGMAIL\@GAPPS.COM/g' \
  --regexmess 's/<OLDGMAIL\@GMAIL.COM>/<NEWGMAIL\@GAPPS.COM>/g' \
  --regexmess 's/Subject:(s*)\n/Subject: (no–subject)$1n/g' \
  --regexmess 's/Subject: ([Rr][Ee]):(s*)\n/Subject: $1: (no–subject)$2n/g' \
  --include '^\[Gmail\]\/All Mail' \
  --include '^\[Gmail\]\/Sent' \
  --regextrans2 's/\[Gmail\]\///' \
# If you want to keep transferred mail in a separate tag/folder
# --regextrans2 's/(.*)/OLDGMAIL\/$1/' \
  --nofoldersizes &
# Use this line instead of the above to dry run and see what folders will go
# --dry --justfolders ;
  
  # Let imapsync fire up and set the hardcoded PID file above in --pidfile
  sleep 10
  cpid=`cat /tmp/imapsync.pid`
  # Peek in periodically to see if we're still running
  while kill -0 $cpid
  do
    sleep 30
  done
done

#Tip: Run like this to log: $> nohup ./sync_mail.sh >>sync.log &