- xxfi_close may be called "out-of-order", i.e. before even the
xxfi_connect is called.
After a connection is established by the MTA to the filter,
if the MTA decides this connection's traffic will be discarded
(e.g. via an access_db result), no data will be passed to the
filter from the MTA until the client closes down.
At that time, xxfi_close is called.
It can therefore be the only callback ever used for a given connection,
and developers should anticipate this possibility when crafting their
In particular, it is incorrect to assume the private context pointer
will be something other than NULL in this callback.
- xxfi_close is called on close even if the previous mail
transaction was aborted.
- xxfi_close is responsible for freeing any resources allocated on a
- Since the connection is already closing, the return value is