Hosting outbound mail for 3 Seperate Organizations

Posted on 2011-04-20
Last Modified: 2012-05-11
Wanted to check in with the forum to validate if the following solution will work.
I have 3 Organizations that do not want to migrate/consolidate operations but need to share a single smtp name space.
Each of the Organizations hosts it's own Exchange 2003 Org and again are currently independent of one another.
I looked into address rewrite and it would require that each Org forwards their outbound mail to a single server acting as a smarthost that will perform the Address ReWrite and then send mail out to the world.
Question: If each one of the Orgs stamps their primary SMTP proxie address with the desired, and forwards to the aforementioned smarthost so that all outbound mail exits from the same system, do we still need to perform the address reWrite?
Question by:Intelli-Po
    LVL 8

    Expert Comment

    I had a similar scenario a few years ago (although we are now 1 big happy company) where we had 3 independant exchange orgs with outsource IT for 2 of them and we had to have a single domain name.
    I did it in a different way as I didnt want to do any manual updates as there were about 25,000 users.

    In the end we used a product called SimpleSync that allowed us to replicate the GAL between all the servers as we needed users to all send with the same SMTP address space but stil be able to mail each other. It does a swap on the primary SMTP address so the contacts use the legacy email address for internal routing.
    The email can then all be delivered to 1 exchange and this would redirect it to the correct exchange based on the SMTP address.
    This enabled each Org to be managed and as we replicated the GAL a few times a day then accounts could create an address that wasnt being used somewhere else without having to engage directly.

    Author Comment

    Sounds like a good solution, I heard of Simplesync and actually did a webinar with them a couple of years ago.
    So, if I am hearing this right, if all the primary smtp proxies match across all the companies, then they forward to one Exchange server for outbound delivery, there is no need to perform and address rewrite?
    Also, I know Simplesynch does the GALsync, does it also do Free/Busy sync as well?
    LVL 8

    Accepted Solution

    this is an example of how we did it (primary email addresses in bold)

    Exchange 1:
    User1, smtp addresses "", ""

    Exchange 2:
    User2, smtp addresses "", ""

    Exchange 3:
    User3, smtp addresses "", ""

    You decide that Exchange 1 is the most stable etc and thats where you deliver mail to from the gateway (any one would work!)
    You enable the swap proxy and replicate:
    exchange 1 to exchange 2 and 3
    exchange 2 to 1 & 3
    exchange 3 to 1 & 2.

    So if you were to look at the GAL on Exchage 1 you would see:
    User1, smtp addresses "", ""
    User2, smtp addresses  "",""
    User3, smtp addresses  "",""

    so if a mail came into exchange1 for Exchange1 would deliver it to Exchange 2 using the internal address - We used an email appliance for inbound \ outbound email so all the exchanges delivered directly to it and it could just do a single LDAP query for inbound address validation etc.

    SimpleSync dosnt do free\busy itself - however since the contacts now exist the microsoft inter org replication tool can then replicate the free\busy info as it uses the smtp address as as the index.
    It works OK and its free - although we had to fiddle about a bit as we also had firewalls between all our exchanges and that made it more fun to get it all working !!!

    When we end up with 6 different exchange orgs replicating to each other before we eventualy migrated to a single AD.

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