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Re: [ietf-smtp] SMTP Status codes

2019-09-04 23:15:37
On 9/4/19 10:35 PM, Geethapriya Liyanage wrote:

The RFC3463 defines new mail system status codes.  However, the excising mail servers are still using old status codes. Is there a work happening to change the current mail systems status codes according to this RFC.

As you have observed, there are two kinds of mail codes.   SMTP "reply codes" are 3 digits long:  2xx is normal, 4xx is temporary failure, 5xx is permanent failure, and so on.   Those reply codes have been with us since at least RFC 821 and have not changed (except that a few new codes have been added).   Those codes affect the SMTP state machine - they tell a client, for instance, whether it can continue the SMTP dialog or whether it should abandon attempts to send the message.

The RFC3463 "enhanced status codes" (note the subtly different name) are intended to provide more detail for delivery and non-delivery reports (also known as "message disposition notifications" or MDNs), and to be language-independent.   There's never been an intention to change the SMTP reply codes, because this would break existing SMTP clients.   But there is an SMTP extension called ENHANCEDSTATUSCODES that allows an SMTP server to return an enhanced status code to a client, for use in an MDN.

When designing the MDN format we realized that the 3-digit SMTP reply code scheme didn't allow for enough different codes to reflect the different reasons for message delivery failure, so we needed a new scheme.

Sorry the similarity between the names is a bit confusing.   In hindsight we probably could have made that a bit clearer.


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