When mobile users experience problems with Exchange Server ActiveSync, it's usually due to a subtle misconfiguration that is difficult to diagnose.
One of the toughest problems to troubleshoot is when Exchange ActiveSync won't download mailbox items to a portable device.
This usually happens if the URLSCAN tool has been used to lock down functionality of the Internet Information Server (IIS) that services Exchange Server's ActiveSync requests.
The URLSCAN utility is used to restrict what types of requests can be sent to or honored by IIS, as a proactive way to prevent attacks or misuse -- for instance, for a Web site that is only being used to honor the most basic functions. That is, the IIS server is not being used to host applications like Outlook Web Access.
If Exchange Server mailbox items are not being downloaded by ActiveSync, there's a chance that the URLSCAN tool was used to suppress the If header, a custom HTTP header used by Exchange ActiveSync.
It's also possible that another device, such as a firewall or proxy, is stripping out such headers, and needs to be configured to allow them through.
Likewise, if certain HTTP verbs are being suppressed, Exchange ActiveSync will not work. You can see a complete list of the verbs needed to allow ActiveSync to run properly in Knowledge Base article 823175, Fine-tuning and known issues when you use the Urlscan utility in an Exchange 2003 environment.
Note that if you have Exchange ActiveSync running on a front-end server, you only need to allow the POST and OPTIONS verbs; running it on a back-end server requires a greater variety of verbs.
About the author: Serdar Yegulalp is editor of the Windows Power Users Newsletter.
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Related information from SearchExchange.com:
Tip: Why HTTP can hurt Exchange ActiveSync attachments
Tip: The Exchange Server ActiveSync Web Administration Tool
Exchange Admin 101: Configuring OMA and ActiveSync
Reference Center: Exchange Server mobile and wireless tips
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