AppSuite:GuardMailResolver
From Open-Xchange
When a Guard user sends an email to a recipient, Guard must be able to determine if the recipient is an OX user, or if that person uses a different email service. If the recipient is an OX user, Guard must be able to determine the users ID and context. This is done through the OX backend by default, which in turn looks up the email address using the default login2context table. Starting version 1.2, Guard can, however, be configured to use a different URL for third party or custom handlers.