Increase the ActiveSync attachment size limit in Exchange
Exchange limits ActiveSync to about 10 MB by default, so large attachments fail to open on mobile devices. Two values in the Sync web.config raise the limit.
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ActiveSync is the Microsoft protocol that synchronises mail, calendars and contacts with mobile devices. Exchange limits its documents and requests to about 10 MB by default. With a mobile device management tool such as AirWatch (now Workspace ONE), larger attachments then simply fail to open.
The limit is set in a web.config file on each Exchange server.
Edit web.config
Open this file in a text editor such as Notepad, after making a backup copy:
C:\Program Files\Microsoft\Exchange Server\V15\ClientAccess\Sync\web.configFind the document size limit, which is about 10 MB:
<add key="MaxDocumentDataSize" value="10240000" />and raise it to about 50 MB:
<add key="MaxDocumentDataSize" value="51200000" />Then find the maximum HTTP request size, set in kilobytes:
<httpRuntime maxRequestLength="10240" fcnMode="Disabled" />and raise it to the same 50 MB:
<httpRuntime maxRequestLength="51200" fcnMode="Disabled" />Restart IIS
The change takes effect once IIS restarts. Use Restart on the server in IIS
Manager, or run iisreset.
Keep an eye on the server
Larger limits can affect the server’s performance. Monitor it after the change and adjust if needed. Microsoft’s ActiveSync troubleshooting guide covers related problems.