Hi Techies,

We have 10 offices (1 HO + 9 sites) with 10 different Domain names. (eg; dom1.com, dom2.com to dom10.com) where dom1.com is the HO. 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.

Now we are planning to move this entire domain to a single domain called "abc.com". So we are really looking for a opensource solution for our entire Infrastructure. If we could propose a good opensource alternative, our Management is ready to accept opensource for its core services. I feel like, this is a great chance to Migrate from MS to Linux... So kindly post your solutions/comments/suggestions.

Existing Infra Details;
1. 9 offices are working with MS Active Directory and its related servers, like Exchange, ISA, etc. and 1 office is using LDAP as the backend and Linux based Servers like Postfix, Squid, etc.
2. Most users are using MS Outlook (few Entourage and Evolution Clients), most operating systems are Windows7 and XP, few are Mac and Ubuntu
3. Outlook Web Access, Outlook Anywhere, Contacts, Calendar are used by users
4. 10% of users are using mobile services (Blackberry, Iphone, symbian, microsoft mobile)
5. We have totally around 2000 users inclusive of all offices.

Objectives of the Expected Solution;
1. Unified single domain called abc.com
2. Linux alternative solution for Active Directory services
3. All sites will be having local Mail servers
4. All External Mails to our company should come to our HO, then re routed to the sites users mailboxes or to the HO internal users mailboxes
5. Each sites users mailboxes should be stored in the local mail server located in that corresponding site
6. When the user is transfered, mailbox should also move to the new location
7. Global Address book should be available from Desktop / web / Mobile devices
8. Should support Blackberry BES service
9. Mail, Contact, Calender, etc should work from Windows, Mac and Linux desktops
10. Web mail support
11. Smooth Migration
- Existing mails should be available in the new setup
- Auto response when a mail hits the old email-id, informing then of the new email-id
- Minimal downtime

We are looking for information to go with a solution which can be used to replace MS with Linux. It will be really helpful if anyone who can share his thoughts/experience to acheive our objectives.

Thanks in Advance...