olemus
mehhanism meilisüsteemi tõrgetest teatamiseks,
informatiivsem algsetest (RFC 821)
protokolli SMPT tõrkekoodidest
=
codes for informing about email system failures

ülevaateid
https://www.iana.org/assignments/smtp-enhanced-status-codes/smtp-enhanced-status-codes.xhtml

https://www.drh.net/blog/what-smtp-replies-enhanced-status-codes-mean-why-you-should-care

standard
https://tools.ietf.org/html/rfc3463