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RE: 4yz Temporary Rejections is part of the SMTP Protocol

2011-10-29 04:32:09

Hi Murray,
At 23:27 28-10-2011, Murray S. Kucherawy wrote:
That's a pretty strong argument in favour of creating something new rather than overloading something old. But that too runs headlong into likely interoperability concerns. There's a bit of induced paralysis there that needs to be overcome.


I would say that it is more about adoption than interoperability. There is also "domain of applicability" to consider. It can help in addressing interoperability concerns or even protocol "violations".

Someone else suggested nothing parses SMTP replies beyond the three digits. That's not true in ESMTP; the enhanced status codes (if used) and the reply to EHLO itself are structured. It's not true in pure SMTP either, where I think some of the replies are specified beyond the three digits (the 220 greeting, the reply to HELO, and the 221 message, as I recall).

The keyword is "structured text".

BTW, you can even get into trouble with assumptions about the three digits being what the specification say they should be as some implementation diverge in their interpretation. The careful reader will take note of the discussion about that.

John suggested a new reply code series, but that scares me a bit; what would a staunch legacy implementation be likely to do with that?

The legacy implementation could ignore it. In practice, it may cause code path issues if there isn't any protocol negotiation.

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