I've just followed the Ubuntu installation guide and then proceeded to migrate my mail from Redhat Sendmail/Pop3/IMAP to Ubuntu 6.06 Server.
There is info in these forums how to do it but scattered about.
Here's a quick migration guide:
You'll need to have IMAP running on your old server. In my case it was present but disabled.
On zimbra server, as root
1) apt-get install build-essential
2) apt-get install make
3) apt-get install libio-socket-ssl-perl
4) Get Mail-IMAPClient-2.2.9 from
http://search.cpan.org/~djkernen/Mail-IMAPClient-2.2.9/
5) Gunzip & untar, and follow instructions in Mail-IMAP/INSTALL to install
6) Download TermReadKey-2.30 from
http://search.cpan.org/~jstowe/TermReadKey-2.30/
7) Gunzip & untar TermReadKey and do same as Mail-IMAP to install (perl Makefile.PL, make, make test, make install)
8) Get imapsync from
http://www.linux-france.org/prj/imapsync/dist/
9) Gunzip & untar imapsync
10) in imapsync dir, use the following command:
./imapsync --nosyncacls --syncinternaldates --host1 old_mail_server --user1 old_server_username --password1 oldserverpwd --host2 new_zimbra_server --user2 new_zimbra_username --password2 new_zimbra_pwd --authmech1 LOGIN --authmech2 LOGIN
You can add --folder INBOX to only sync the inbox folder. And there are other options too, ./imapsync to display the help
Yes you need to run imapsync for each user, but this can be scripted.
Bertie