I was having an issue with some email being delivered to some distribution groups. I started looking into the issue and found some interesting information.
A quick rundown of the environment. We have one forest with 2 domains. We currently have a mixed 2003 and 2010 Exchange environment, one 2003 server and one 2010 server. We currently have 3 sites.
Site 1 - All machines are part of domain.com (including several DCs for domain.com), with exception of one DC that is a DC for subdomain.domain.com.
Site 2 - All machines are in domain.com, and contains 2 DCs for domain.com
Site 3 - All machines are part of subdomain.domain.com, including 2 DCs for subdomain.domain.com
Now the issue that we were having was that some emails sent to this DL were received, some were not. I looked into this issue using message tracking. I found that all of the emails sent to this DL, DL1@domain.com, were being received by the 2010 server. However not all of the emails were being received by the members of this list. I found several messages sent to DL1@domain.com that failed to expand the user correctly, because instead of using the DC that was part of domain.com, it was using the DC that was part of subdomain.domain.com.
Now I found that DL1@domain.com was not a universal DL, and that seemed to be what was causing it to fail. Changing it to a Universal group now expands correctly even when it is expanded against the DC that is part of subdomain.domain.com.
Now after seeing this, I have a few questions about how this process is handled to make sure that I dont have further issues.
1. How does Exchange 2010 decide what DC to use? From what I can tell it just takes whatever DC responds first in the site that it is located in?
2. Will this cause any issues with users that are in domain.com, if it expanding or routing against the DC from subdomain.domain.com? (I am assuming that users and groups are handled differently because I dont see any issues with the users)
3. What is the best practice here? I realize now that I should probably convert all of my DLs to Universal groups, does this sound correct?
Any other recommendations or input about things that I may be missing?