The EcpUrl-extinstall element contains a value that, when appended to the value of the EcpUrl element (section, results in a URL that can be used to view or change the mail add-ins currently installed in the user’s mailbox. It is an optional child element of the Protocol element (section<18>

The value of the EcpUrl-extinstall element is similar to the following: "Extension/InstalledExtensions.slab?exsvurl=1&amp;realm=contoso.com".