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[ietf-smtp] SMTP status codes 251 and 551

2020-02-10 10:04:43
SMTP has had the 251 and 551 status codes for a long time, since RFC 788 in 1981. The 251 code means (roughly) I'll accept this address but I'll forward it to <x>, and 551 means address rejected, send it to <x> instead. The idea is that the sending system should note the <x> address so in future it sends mail directly there.

Did anyone every actually implement these, and in particular the sender side to remember and redirect? You don't have to tell me all the reasons it's a bad idea, many of which are described in the RFCs. I'm just wondering whether this was ever real, or it just seemed like a good idea.

John Levine, johnl(_at_)taugh(_dot_)com, Taughannock Networks, Trumansburg NY
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