iPhone 4 and ActiveSync error

Problem:  A client recently had an issue with their Exchange 2003 server experiencing a problem with ActiveSync for several weeks/months.  ActiveSync functionality sporadically stopped and the following errors showed in the Application log:

Server ActiveSync Error Number 3007:

Exchange mailbox Server response timeout: Server: [...] User: [user@domain.com] Exchange ActiveSync Server failed to communicate with the Exchange mailbox server in a timely manner. Verify that the Exchange mailbox Server is working correctly and is not overloaded. 

Server ActiveSync Error Number 3005

Unexpected Exchange mailbox Server error: Server: [...] User: [user@domain.com] HTTP status code: [500]. Verify that the Exchange mailbox Server is working correctly.

A quick fix of restarting the IIS services resolved the issue but only for a few hours.

Also Apple's fix appeared to help again only briefly the issue was still there.

After much investigation the issue pointed to a performance problem on the Exchange Server.  The resolution was to run Microsoft's Exchange Best Practices Analyzer and address the issues it reported.

In this case prime issues were relating to:

'HeapDeCommitFreeBlockThreshold' not set.

Server has 1 GB or more of memory, accommodates [X number of] mailboxes, and the 'HeapDeCommitFreeBlockThreshold' parameter has not been set to [Y number].  Virtual memory may become quickly fragmented and system instability may occur.

(We set the threshold)

Paging file larger than physical memory.

The space for the paging file [XX number] is larger than the physical memory [YY number].  This may affect the system performance.  It is recommended to have paging file size equal to the physical memory.

(We changed the page file to match the physical memory size)

Virus Scanning API (VSAPI) low thread count.

The number of virus scanning API threads on server is too low and may cause performance degradation. Current number of threads: 3. Based on the current hardware configuration, a value of 9 is recommended. (We changed to 9)

Virus Scanning API (VSAPI) background scanning.

Background antivirus scanning is enabled.

(We disabled it)

Exact IT Solution:  After carrying out the above steps and rebooting the server, we carried out further tests and ActiveSync was no longer causing timeout errors.