I was using the following technique
imapsync --dry --host1 OLD_MAILSERVER --ssl1 --user1 OLD_MAILUSERNAME --passfile1 ./oldpasswd.txt \
--host2 NEW_MAILSERVER --ssl2 --user2 NEW_MAILUSERNAME --passfile2 ./newpasswd.txt
I have about another 10 mailboxes to migrate...
enter R2 Unit
Help me OpalStack, you're my only hope...