Send BOUNCE(IFYOUMUST), virus notifications, and other messages from null <> sender to avoid bounce loops.
Test sender alignment: MAIL FROM different than "From:" mail header Address book whitelisting that does NOT rely on Registry Keys HLM\software\softalk\WorkgroupShare\setup\DBType HLM\software\softalk\WorkgroupShare\setup\dataFolder It should use (or at least fall back on) an ODBC DSN. Test for to indicate the "width" of IP4 mask in a SPF records, +all would be 31, +IP4:./2 would be 29, +IP4:./24 would be 7. No use of masks would be 0. At minimal a test to check existence of DMARC policy (possibly even honor policy as much as applicable to Declude)
