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bignose
Asked: 2017-03-17 10:36:12 +0800 CST

SMTP response for unspecified system error

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What SMTP response code and message should be used for an unspecified system error in processing the request?

RFC 5321 §4.2 states:

An SMTP server SHOULD send only the reply codes listed in this document. An SMTP server SHOULD use the text shown in the examples whenever appropriate.

What should an SMTP server implementation do for an error that does not fit any of the listed codes and descriptions?

The HTTP specification has a response code 500 for a non-specific “Internal Server Error”. What is the appropriate SMTP equivalent that stays within the bounds of the above “SHOULD” admonitions?

smtp

1 Answers

  1. The more correct return code for generic errors seems 451

    From the RFC:

    451 Requested action aborted: error in processing

    If you, for some reasons, feel that 451 is not adequate, you can use 430 or 440:

    4yz Transient Negative Completion reply

    x3z Unspecified.

    x4z Unspecified.

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