Welcome to the forums,
FYI the forums entail free community based help, paid users have additional support sites - though I realize you haven't purchased yet / of course it's in their best interest of sales@ members to browse here as well.... (they do have Service Engineering/Professonal Services people to address these questions).
Anyways, touching on a few of the bigger points:
>Some of of the sites are using Ex2k3 + AD, some are Ex2k7 + AD and one site is postfix + ldap, and few sites are having hosted mail service.
Migration wise:
Migrating from Microsoft Exchange to Zimbra Collaboration Suite User Migration - Zimbra :: Wiki
You also have to decide how you want to do auth, against Zimbra (built in LDAP) or another external LDAP/AD.
Server service wise (and I won't speak to hardware sizing specifications just yet, 5-10GB that incoming or intra? and 7-25mb is a good start but do we have volume # info, peak in x time etc? ie things that may prompt consideration of a 2nd zimbra mta instance etc - and definitely give the HO a nice box)
HO: (All services)
LDAP Master (openldap)
MTA (postfix)
AntiVirus (amavisd + spamassassin)
AntiSpam (amavisd + clamav)
Store (aka mailboxd - jetty + mysql + lucene etc etc)
Logger
Convertd (if NE, this lets you view documents as HTML using an apache engine)
Stats
Spell (apache aspell checker for the web-client)
(SNMP if desired)
Do you want to consider HTTP/IMAP/POP proxies (ngnix/memached) as well? This hides the server names etc. Even without proxy they can still hit a generic mail.domain.com url for the web-client and be routed to their proper box at sign-on, but without proxy you'd have to configure thick clients accordingly. Cons would be more single points of failure/traffic to HO. But note you can also treat HTTP and IMAP/POP separately (ie turn it on for only one type).
I'd start by reading:
Working with Zimbra Proxy
Also:
Configuring IMAP and POP Proxy Server Configuring ZCS HTTP Proxy
>All External Mails to our company should come to our HO
Simple, point the DNS MX record for the domains (10/11?) involved at the HO server(s).
LO's:
LDAP Replica (to reduce lookups to the master/more self sustaining if HO unreachable)
Store
Spell
Convertd (if NE)
MTA (Again you don't have too, but if you want them to function on their own. If you always use it for outgoing to reduce load on HO (rather than just manual flip over during outages) be sure any SPF rules in DNS cover it etc.
>4. Each sites users mailboxes should be stored in the local mail server located in that corresponding site
>8. When the user is transfered, mailbox should also move to the new location
zmmailboxmove
>5.All mails to HO and Sites should be centrally backed up from the HO.
>6. easy recovery of individual mails
CLI zmrestore restoreToTime Network Edition only - Zimbra :: Wiki
Again there's plenty of open source solutions too
Backup and Restore Articles - Zimbra :: Wiki
>7. Should have a quick disaster recovery
Start by defining 'quick' at your business. HA and BCP discussions are a matter of what you can afford server wise, the time you can afford in outages, what things are critical, where your storing the backups (are you grabbing all system & /opt/zimbra directories or just talking ZCS's built-in hot backups etc). Is each LO gonna get their own copy of their own server/mail or just the HO? If just mounting 10 /opt/zimbra/backup dirs on the HO EMC SAN don't forget bandwidth restore time - I've seen people with backups down the the second, but didn't account for site wide restores that would take several weeks.
Whether that's multiple ldap copies, multiple mta's, standby/clustering/drbd servers for mailstores etc, there's also some server-to-server sync solutions in the works and other full global solutions being discussed. So for the above I'm pretending you just have 10 ZCS servers/1 per site, please read through some other threads and work out a solution you're comfortable with.
>10. Should support Blackberry BES service
If you want push there's open source wise there's solutions like Funambol, if going network edition there's Mobile Sync. (ActiveSync support for iPhone/Android/WM/whatever) For Blackberry there's ZCB (requires another win box for BES of course).
>12. Mail, Contact, Calender, etc should work from Windows, Mac and Linux desktops
IMAP, POP (if you really have too), Zimbra Desktop, there's also ZCO if you want to quickly add support for things besides standard mail functions to outlook (opinions of this connector vary).
>13. Web mail support
There's basically 3 (well a few more) experiences web-client wise right now: Advanced AJAX, Standard/Lite HTML (for the most part), and Mobile Web.
>9. Global Address book should be available from Desktop / web / Mobile devices
Check. (ease of setup so depends on client, auto in mobile sync/ZCO or pointing at an ldap url in TB etc)
>11. Should support Calendering
Check. (big CalDAV supporters)
>14. Feature like Single Instance Storage for optimal storage in case of multiple instance of a mail
This is available per mailstore (uses hard links) if the message is delivered at the same time. ie LO1user1 emails LO1user2 LO1user3 LO1user4 HOuser1 LO2user1 > that's 3 copies).
>Auto response when a mail hits the old email-id, informing then of the new email-id
Have a read of
Managing Domains - Zimbra :: Wiki
The easiest would be to drop your requirement for the auto-response, and instead focus on deliverability to the new account (aliases & catchall sections in above doc).
Replies would then come from the new domain (or can even have it auto appear as the old domain name when they reply aka masquerading but I'd avoid that since you want to spur usage of the new).
If your really intent on the message back to the sender you're going to be talking variations of either:
A) Point the MX's for those old 10 domains at the new main MTA and setup a catchall > mapped to 10 or so accounts with generic out of office messages set telling them to send to
same@newdomain.com
B) Creating a distribution list per old address (while free that's still 2k lists) > mapped to 10 or so accounts with generic out of office messages set telling them to send to
same@newdomain.com
C) Provision 4k users > each with a FWD to proper address and an OOO message specifying "Your mail to
user@olddomain.com has been delivered to
user@newdomain.com, this is just to let you know so you can watch for a reply and update your own contact book." = more $ See
https://buy.zimbra.com for a basic check, but you should contact sales for a actual quote, especially if in edu/gov sector.
D) Additionally you can setup things in zimbra's postfix (but not in the zimbra ldap itself) but we won't discuss them here right now as outside of NE support, easier 'management wise' would be the next option:
E) Setup a standalone open source edition server (talking a separate ldap instance/will be managed in a different admin console etc) to handle all the old domains (with every account provisioned and fwd to new domain etc)