we're still on CU4 as installed. i believe it's up to CU9 now. question is, where do you apply this CUs? CAS or Mailbox server? or both?

General guideline is that you should apply CU to all server roles, mailbox, CAS and edge (if you have).

• Proposed as answer by Edward van BiljonMicrosoft community contributor, Moderator 16 hours 8 minutes ago

If you're referring to which roles should be targeted in what order, it no longer seems to matter anymore in Exchange 2013. This is no longer emphasized nor mentioned in the CU release articles to my knowledge, unlike for previous Exchange versions (section "Proxying between Client Access Servers here).

hi

you would apply it all servers so they all on the same patch level. start with your internet facing CAS first and then move to your mailbox servers.

General guideline is that you should apply CU to all server roles, mailbox, CAS and edge (if you have).

• Proposed as answer by Edward van BiljonMicrosoft community contributor, Moderator Sunday, July 12, 2015 3:21 PM
• Marked as answer by Reno Mardo 18 hours 15 minutes ago

Hi,

Document for reference, upgrade Exchange 2013 to the latest cumulative update or service pack

https://technet.microsoft.com/en-us/library/jj983803(v=exchg.150).aspx

Best Regards.