I have four sites which in involved in this current issue. Site A,B,C&D, in each site there is one exchange 2007 HT server
There is direct communication from site A <-> B & A<->C & from C <-> D, but there is no direct connectivity b/w A to D. Currently mail from A to D goes to B and reaches D. I want mail flow from A to D through C only.
Both C and D are behind the firewall in separate network and belongs to different domain under the same forest. C is in root domain & D is in another child domain. All are using exchange 2007 SP1, windows 2003 AD.
To make mail flow from A to D only through C, I shut down HT server in site B, thinking it will take the alternative path i.e. through C, but I found that mails get stuck in site A HT itself. Then I tried creating AD site link with lesser cost than other paths from site A to site C (This was not there before). But still mails gets stuck in site A HT queue itself. During the same time, I tried sending a mail from site A to site C mailbox and it goes through without any issues as there is direct connectivity, but mails from A to D is not flowing through C.
As I understand exchange 2007 first tries direct connection to route the mails, if direct connection fails it falls back to AD site link cost to determine the alternate best path. I observed in the routing log viewer that the cost is calculated based on the AD site link cost, I cross verified by changing the cost. So there is no issue in calculating the cost. But still the mails remain in site A HT. When I checked connectivity log on site A HT,it shows that site A HT has tried to connect site D HT but there is no direct connection then it tries to connect to site B HT which I have manual shut it down. Now it continues to try and connect to site B HT and never tries to connect to site C HT even though site link cost is less. I tried to set link cost for exchange using set-adsitelink command , but this also did not help.
I am not able to understand what is wrong. I know if I open direct communication b/w site A and site D then there will be direct mail flow, but I want to make it work through site C and also want to understand why it is not falling back on alternate path when the communication path is available. Can someone please guide on this.