In Microsoft Exchange Server 2013, there are several different message size limits that apply to messages as they travel through your Exchange organization. For more information, see Message size limits.
However, there are client-specific message size limits you can configure for Outlook Web App and email clients that use ActiveSync or Exchange Web Services (EWS). If you change the Exchange organization-wide message size limits, you need to verify that the message size limits for Outlook Web App, ActiveSync, and Exchange Web Services are set accordingly. You configure these values in web.config files on Client Access servers and Mailbox servers. These limits are described in the following tables.