We just migrated from an old version of FirstClass (Old OS 9 version). We didn't use the calendaring so I only needed to be concerned with mail. We are a small business with just a few mailboxes so the migration while sometimes difficult wasn't as painful since I only had about 25 mailboxes to migrate. Took me a weekend to complete the job.
I ended up using imapsync-1.219 (freshmeat.net
: Project details for imapsync) which is a perl tool to move mail from FirstClass to Zimbra. Again this is very specific to our FirstClass server...I was not the admin of that box so I can't tell you the version number but I can find out and get back to you if needed. I also found that my tools needed special commands to limit the IMAP retrievals... here is the command I used.
./imapsync --nosyncacls --subscribe --syncinternaldates --host1 firstclass.mailserver.com --user1 userlogin --password1 'userpassword' --host2 zimbra.mailserver.com --user2 email@example.com
--password2 'userpassword' --authmech2 PLAIN --ssl2 --folder 'INBOX' --split1 10 --split2 10 --debug
Some important gotchas with our FirstClass migration.
1) If your users created folders inside their mailbox and files mail in those folders they are not accessible via the IMAP interface. It may be the older version we had or it might be that way with all the versions.
2) In our version only received mail was visible via the IMAP interface. So in our migration we had our users move any mail from their mailbox folders back to their mailbox. And just lived with the fact that send mail could not be migrated.
3) Because the way FirstClass handles IMAP I couldn't go back and sync the mail. Meaning if I ran the migration script again it would duplicate the messages. I attempted to get around this but decided to just turn off the firstclass smtp agent so it couldn't accept anymore mail after I changed the DNS settings.
All my users are happy as clams now with Zimbra and really enjoy using it.
I hope this helps a little.