We have the short term need to setup an SMTP Shared Namespace on a single email domain.
At the moment the primary MX is setup to send mail to O365 first. Then O365 has an Internal Relay setup to point to an Exchange 2007 for any addresses not local to O365. Obviously the Exchange 2007 box has the same internal relay setup to cover internal mails for users based back on O365.
Mails addressed to specific people works fine between servers as does incoming mail from external users to the new domain.
My question is how to cover a distribution group that is split across sites.
Rather than adding 100 odd mail contacts at each site, we figured the best way would be, for each cross site list, to have a group at each site with two SMTP addresses, one for shared domain.com and one for nonshareddomain.com.
I then figured if we setup mail contacts at the opposite site to have a contact for firstname.lastname@example.org it would cover it i.e
email@example.com contains a list of local users to the local mail server.
On O365, that list also includes a contact for firstname.lastname@example.org
That way, if an O365 user sends a message to everyone@, that message gets relayed to the other site, which in turn distributes it to all the other sites local users.
However, am I right in thinking that if we have a smiler relay contact setup in everyone@shareddomain in the other site, we will potentially create an infinite loop, as it will be trying to send back to email@example.com at the first site.
Hope this ramble makes sense.