Checked: If a custom MAPI transport is installed, Outlook polls the transport when a message for that transport is submitted, ...

Checked: If a custom MAPI transport is installed, Outlook polls the transport when a message for that transport is submitted, even if Outlook is working offline. | Unchecked: When Outlook is working offline, a message submitted for a custom MAPI transport is not sent until the user performs a Send/Receive.