Hey, wait a minute...we're in Florida (Tampa) and RFCs mean something here...<grin>
The RFCs mean something only to people who want them to. In the muddy trenches of the spam war, RFC boot-polishing niceties are irrelevant.
Rejection all null senders is clearly a bad idea, but so much spam uses null senders, the temptation is just as clearly present.
To catch a large number of spam with MAIL FROM:<>@sender.domain, I sometimes use null sender as a condition to apply other tests:
If MAIL FROM:<>, then reject if:
no PTR (includes requiring matching A record)
HELO hostname not found in DNS
helo domain.tld is 2-letter TLD (excluding .us and .ca for N.A. MXs)
helo domain.tld is a "subscriber" network domain name.
Else, accept (for this test only, more tests to follow)
Len
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