How to Set an Expiration for an Outbound Message

You can set an outbound message to expire after a specified number of
minutes. This will cause the message to fail if it cannot be delivered
in the specified amount of time. This is controlled by a special
X-xsExpire header which you add to your outbound message.

The value of this header should specify the expiration time in
minutes. When the outbound message is injected, this value will be
added to the local server time and stored with the message. The stored
value will be checked before any delivery attempt, and if it is prior
to the current server time, the message will be failed. See example
below.

X-xsExpire: 20

This header will be removed before the outbound message is delivered.