Firsts Steps to Migrate from postfixadmin.
The password of ispconfig is the same of postfix admin.use crypt function.
I working on migration.
Writing a php console script to do select on postfixadmin usertable and inserts on ispconfig3 tables.
you only need select quota and password and insert or update existing mail account on ispconfig 3 tables.
diretory schematics is verry simillar exepts for one thing.
basedir it´s your choice at postfixadmin setup.
postfix admin use:
you need make a automated rotine to move
/basedir/domain.com/user/Maildir to /var/vmail/domain/user
before moves maildir data you need change recursively all files and folders to vmail user and vmail group.
chown -R vmail:vmail /var/vmail/
all files without vmail user and group will be changed to vmail user and group.
I migrate one mailbox to test works perfectlly.
I prentend use this tecniques to migrate from postfixadmin to ispconfig3.