:post-delivery-function

Keyword

Default value: nil

When non-nil, the value post-delivery-function should be a function designator for a function of one argument:

The system calls post-delivery-function after delivery. successp is true if delivery was successful and false otherwise.

Note: during the delivery process, the Lisp system can be in an unstable state, so it is not always possible to recover when delivery is not successful.