Route mail and Active Directory Sites and Services configuration

Question

Folks,
I have a problem in the internal email routing. My network is spread across various regions and the branch offices are connected together in a mpls network (full mesh). Every region has its own Exchange Server with all roles installed and the smtp connection
to the outside world is linked to two Exchange servers in the headquarter server farm.
The problem is that internally I often see emails going across the Exchange Servers in the branch offices where there is low bandwidth (from 3 to 5 Mbps), thus email are sent first to these servers instead of going immediately to the Exchange hosting
the mailboxes of the intended recipients. This happens also with inbound emails.
This causes slowness in the email system and sometimes also the network with these branch offices suffers from packet loss or very high latency.
I know that Exchange is a site-aware application and uses the Active Directory topology for message routing and to communicate with the services that are running on other Exchange 2013 computers. For this reason I have checked the Active Directory Sites
and Services and surprisingly I have found that there are no sites, no subnets, nothing has been defined but the default settings, included the Inter-Sites transport which contains the default DEFAULTIPSITELINK.
Apart from the fact that clients use logon servers which are not supposed to use in the far remote offices, I am concerned of changing the Exchange Infrastructure whilst the email system is running and I would like to ask your opinion about my next steps:
1) Create subnets for every office
2) Create sites and then link them to the subnets done in point 1
3) Delete the DEFAULTIPSITELINK and create new site links based on the costs (network speed) in order to determine the best routing server. I have 5 remote offices with 5 different network bandwidth, so I'll have to create 5 IP site links: high cost for
link with slow network, low cost for fast network.
4) (Optional) Configure the Exchange-specific cost using the Set-AdSiteLink cmdlet to the AD IP site links created previously
Apart from the valid questions on why the previous Exchange Administrator have forgotten to set up the Active Directory (Topology) Sites and Services...
...And why have chosen to install all Exchange Roles to each server when there was no reason to do that (there are two servers connected to the external smtp gateways in the headquarter, so in my opinion the Exchange Servers in the remote branch offices
should have had only the mailbox and the cas role)...
As a matter of fact, my idea is to go further and create the sites,subnets and the ip site link. If I still notice a wrong email flow, I can configure an ad-hoc Exchange-specific cost using the Set-AdSiteLink cmdlet. Does this sound reasonable to you guys
or I am taking the wrong decisions?
Thanks

Answer 1

Thank you very much for your link. This is exactly the page I have read just before posting my question here. It is not easy for me to understand why this has been setup this way by a Microsoft certified engineer.
There are specific rules to follow when Active Directory and Exchange are located in multiple sites and I am not a skilled Exchange Administrator... he keeps saying that it is correct and also tells that if I go forward with my ideas there is the
risk to increase the level of complexity. I prefer more complexity than default setting, and as a consequence of that, connectivity problems!
Hopefully everything goes well. I will post my results here once I have done the changes
Regards