Few sites one company how to connect ?!

Hi all !
I have been asked to connect 3 sites of excahnge server (one is UK one is US on in IL)
later on those exchange (or one of them) should handle pop3 and SMTP to the world not just internal.

I need suggestions on how i should do it cleanly and secure, i got the picture that only one should be connect to the pop3/ smtp and be the main DNS and a recipent or followup of other mailbox to other sites should be done ....
open to suggestion !

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Since you have multiple sites, I would recommend one of two scenarios (not having quite all of the details)

1. Set up a single IMC to point to your primary SMTP mail relay (internal or ISP)  Set your MX records on the respective relay to point to your IMC for delivery.  Recalculate the routing so that IMail traffic flows accordingly.

2. (my preffered scenario) Set up an IMC for each site pointing to the primary SMTP relay that hosts your company domain.  Create an alias table on your relay to resolve inet addresses to Exchange directory names @ the respective Exchange server with a cost of 10 and other(s) with a cost of 20.  This way if your primary IMC goes down, it can re-route internally off of your Exchange directory and through your internal connector(s) (x.400, site, etc)

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