Takže na zcela přesnou technickou otázku zní odpověď (omlouvám se jestli nebudu citovat zcela přesně) "základní normy jsou k ničemu, ať žije Divoký Západ"?
Jinak čistě mezi náma, i rfc5321 ochranu před spamem zmiňuje. Dovolím si citaci, ke které opravdu není co dodat:
"As discussed in Section 7.8 and Section 7.9 below, dropping mail
without notification of the sender is permitted in practice.
However, it is extremely dangerous and violates a long tradition and
community expectations that mail is either delivered or returned. If
silent message-dropping is misused, it could easily undermine
confidence in the reliability of the Internet's mail systems. So
silent dropping of messages should be considered only in those cases
where there is very high confidence that the messages are seriously
fraudulent or otherwise inappropriate."