added POD description of spfquery note
changed spf_deny -> reject (and offered 4 more options, see POD for reject)
backwards compatible with old config settings
replicates qmail-smtpd SPF patch behavior
improved logging (again)
uses a stringy eval 'use Mail::SPF' in the register sub. If missing, warn and log the error, and don't register any hooks. This is much nicer error than the current, "*** Remote host closed connection unexpectedly." broken mail server that results from enabling the SPF plugin without Mail::SPF installed.
background: I noticed I was deferring valid emails with the SPF plugin at 'spf_deny 1', and without changing the code, there wasn't a way to change how ~all records were handled. This provides that flexibility.
