I was working today with a sysadmin who is replacing squirrelmail/qmail-ldap/openldap with Zimbra. His requirement is that he's able to move a few users at a time, while running both systems in parallel.
With the following backend changes the end user doesn't need to change IMAP/SMTP settings in Thunderbird/Outlook/etc.: the qmail server will forward smtp and imap connections over to the Zimbra server. The Zimbra server will accept the connections using qmqpd.
Once the system-wide config change is made, individual users can be switched back and forth between qmail and Zimbra simply by modifying their mailHost in LDAP.
Disclaimers:
- This will not migrate/sync old mail.
- Mail for end user will be delivered to either qmail or zimbra, not both. Getting a local copy into qmail before handoff to Zimbra is left as an excercise for the reader...
- Your Schema May Vary!
- This is for SMTP/IMAP only: webmail users must go to a new URL. Or perhaps you can figure out how to make "Login" button of legacy system do an ldap query and redirect to Zimbra on a per-user basis...
Here's what he did:
In Zimbra postfix:
master.cf
-----------
628 inet n - n - - qmqpd
(just uncomment the existing line)
main.cf
---------
qmqpd_authorized_clients = 10.10.10.0/24
qmqpd_error_delay = 1s
qmqpd_timeout = 300s
(Add at bottom, set clients to qmail mta's)
For each users qmail-ldap ldap entry (mailHost is key part):
dn: cn=customer@example.com,dc=example,dc=com
cn: customer@example.com
sn: customer@example.com
objectClass: qmailUser
objectClass: exampleUser
objectClass: person
mail: customer@example.com
mailHost: zimbra.example.com
uid: customer@example.com
deliveryMode: nolocal
deliveryProgramPath: /usr/local/bin/maildrop -d customer@example.com
mailQuotaSize: 104857600
mailQuotaCount: 10000
mailMessageStore: /home/example/a/customer@example.com
userPassword:: e2NyeXB0fSQxJHJvJHpuSEQwbmlXb2JselZiNTVhbkpFWC4=
customerId: 222236
