|A DKIM_PSTATE is an opaque structure which contains state
information with respect to policy lookups.
DKIM policy evaluation is a multi-step process which can involve several
queries to look up SSP or other information about a sending domain. When
a policy lookup callback is in use
the callback might be unable to complete a particular lookup and thus
return DKIM_CBSTAT_TRYAGAIN. In such cases, it is likely
desirable to resume the incomplete policy lookup when the calling
application knows it can complete the query. The DKIM_PSTATE
is a state structure which is loaded with information required to resume
a policy evaluation where a callback caused it to be suspended.
Before use, it should be allocated by the caller and cleared using
bzero() or memset().