Did you know that Exchange ActiveSync has different message size limits to those set on individual mailboxes or at the Mailbox Database or Organization level. Having these limits set incorrectly can cause issues when attempting to send attachments from a mobile device in an Exchange on-premises or hybrid environment. For more details, see Configure client-specific message size limits in Exchange Server.
Inspecting or modifying these message size limits requires manual editing of configuration files. The ActiveSync Client Limits Tool provides a graphical user interface which allows Exchange ActiveSync Client Limits to be quickly and easily inspected and updated. Note that these settings are per-server, and the tool will need to be run on each Exchange Server to inspect and/or update the message size limits.