Compatibility between Exchange 2007 service packs

Question

Hi all, I have 5 servers Exchange:
- 3 Servers CAS and HUB
- 2 Servers Mailbox server in Microsoft Failover Cluster (MSCS)
Domain Controllers are all
Windows Server 2003 SP2
The versions of Exchange 2007 SP1 servers are all:
8.1 Build 240.6
I have thought about installing SP3 and RU13 in all 5 servers for Exchange, but I'm going to install SP3 and RU13 on 2 servers CAS / HUB and the following week at the other CAS / HUB server.
Finally, the following week in the two Mailbox Servers.
Is there any problem if I miss 2 servers CAS / HUB with SP3 RU13 and the other CAS / HUB in SP1, this will only be for a few days?
Is there any problem if I leave the servidors Mailbox Servers in SP1 while CAS / HUB are in SP3 RU13, this will only be for a few days?
regards
Microsoft Certified IT Professional Server Administrator

Answer 1

Hi Yupikaiey.
Only thing you should be concerned is if you have CAS-CAS proxy or the Mailbox Cluster part.
Your current plan looks good. Just stay alert for any uncommon issues popping up, which would normally mean due to the difference.
If you upgrade your servers in this order, you may avoid potential service interruptions.
Details below:
Version Constrains are more of between roles of 2007-2010-2013 and not between same version SPs or RUs.
Exchange 2013 Server Role Architecture
The Past: Exchange 2007 and Exchange 2010
Our goal was to make these server roles autonomous units. Unfortunately, that goal did not materialize in either Exchange 2007 or Exchange 2010. The server roles were tightly coupled along four key dimensions:
2.This also necessitated a tight versioning alignment – a down-level Hub Transport or Client Access shouldn’t communicate with a higher version Mailbox server; in some cases this was enforced (e.g., Exchange 2007 Hub Transport servers cannot deliver messages
to Exchange 2010 Mailbox servers), but in other cases they were not (e.g., an Exchange 2010 SP1 Client Access server can render data from an Exchange 2010 SP2 Mailbox server).
The versioning restriction also meant that you could not simply upgrade a single server role to take advantage of new functionality – you had to upgrade all of them.
The Present: Exchange Server 2013
If I upgrade the Mailbox server with a service pack or cumulative update, then for a given mailbox hosted on that server, all data rendering and content conversions for that mailbox will be local, thus removing version constraints and functionality issues
that arose in previous releases.
Exchange 2007 Servicing
http://technet.microsoft.com/en-in/library/dd421853(v=exchg.80).aspx
Deployment Order
Our test infrastructure guarantees that Exchange hotfixes work across multiple server roles. The order in which you apply the update rollup to the servers is not important except if you are deploying CAS-CAS proxying. Because the update rollups are not segmented
for different Exchange server roles or for specific file configurations, apply each update rollup package to all Exchange 2007 servers in your environment.
If you have multiple Active Directory sites, and if you deploy a Client Access server in the proxy sites that do not face the Internet, you must
apply the update rollup to the Internet-facing Client Access servers
and to the non-Internet-facing Client Access servers in the proxy site simultaneously. For other Exchange 2007 configurations, we recommend that you
apply the update rollup package to the Client Access servers before
you apply it to servers that are running other Exchange 2007 server roles, such as the Mailbox server role, the Hub Transport server role, and the Edge Transport server role.
Note:
Applying service packs and update rollups to clustered Mailbox servers requires specific planning and application steps. For more information about how to apply service packs to Exchange 2007 clustered Mailbox servers, see
Upgrading Clustered Mailbox Servers to Exchange 2007 SP1 or later. For more information about how to apply update rollups to Exchange 2007 clustered Mailbox servers, see
Applying Exchange 2007 Update Rollups to Clustered Mailbox Servers.
For Patching and compatibility between versions:
Determine the service pack level of Exchange. 
Update rollups are service pack dependent. For example, an Update Rollup 5 package is available for Exchange 2007 and for Exchange 2007 Service Pack 1. To determine the service pack level of Exchange, examine the
ExchangeVersion property. For more information about how to view the
ExchangeVersion property and about the build number that is associated with each Exchange version, see
Exchange Server 2007: Platforms, Editions, and Versions.
References:
How to Install the Latest Service Pack or Update Rollup for Exchange 2007
Exchange Server Updates: build numbers and release dates
We are looking at doing the roll-up to SP3
Coexistence of Exchange2007 SP1 and Exchange 2007 SP3
Regards,
Satyajit
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