Issue #11388 has been reported by Evgeniy Serykh. ---------------------------------------- Feature #11388: SMTP Service Extension for Delivery Status Notifications https://bugs.ruby-lang.org/issues/11388 * Author: Evgeniy Serykh * Status: Open * Priority: Normal * Assignee: ---------------------------------------- Considering https://tools.ietf.org/html/rfc1891 and http://www.sendmail.org/~ca/email/dsn.html TD;DR SMTP session via Telnet: `R: 220 Pure-Heart.ORG SMTP server here S: EHLO Pure-Heart.ORG R: 250-Pure-Heart.ORG R: 250-DSN R: 250 SIZE S: MAIL FROM:<Alice / Pure-Heart.ORG> RET=HDRS ENVID=QQ314159 R: 250 <Alice / Pure-Heart.ORG> sender ok S: RCPT TO:<Bob / Big-Bucks.COM> NOTIFY=SUCCESS,DELAY ORCPT=rfc822;Bob / Big-Bucks.COM R: 250 <Bob / Big-Bucks.COM> recipient ok S: RCPT TO:<Carol / Ivory.EDU> NOTIFY=FAILURE ORCPT=rfc822;Carol / Ivory.EDU R: 250 <Carol / Ivory.EDU> recipient ok S: RCPT TO:<Dana / Ivory.EDU> NOTIFY=SUCCESS,FAILURE ORCPT=rfc822;Dana / Ivory.EDU R: 250 <Eric / Bombs.AF.MIL> recipient ok S: RCPT TO:<Fred / Bombs.AF.MIL> NOTIFY=NEVER R: 250 <Fred / Bombs.AF.MIL> recipient ok` Now **Net::SMTP#rcptto** looks like this: ` def rcptto(to_addr) if $SAFE > 0 raise SecurityError, 'tainted to_addr' if to_addr.tainted? end getok("RCPT TO:<#{to_addr}>") end ` It's impossible to use SMTP Service Extension for Delivery Status Notifications in current implementation? -- https://bugs.ruby-lang.org/