电子邮件客户端软件开题报告+论文+源代码+英文文献 第5页
C: EHLO jgm.example.com
S: 250-smtp.example.com
S: 250 AUTH CRAM-MD5 DIGEST-MD5
C: AUTH FOOBAR
S: 504 Unrecognized authentication type.
C: AUTH CRAM-MD5
S: 334
PENCeUxFREJoU0NnbmhNWitOMjNGNndAZWx3b29kLmlubm9zb2Z0LmNvbT4=
C: ZnJlZCA5ZTk1YWVlMDljNDBhZjJiODRhMGMyYjNiYmFlNzg2ZQ==
S: 235 Authentication successful.
5. The AUTH parameter to the MAIL FROM command
AUTH=addr-spec
Arguments:
An addr-spec containing the identity which submitted the message to the delivery system, or the two character sequence "<>" indicating such an identity is unknown or insufficiently authenticated. To comply with the restrictions imposed on ESMTP parameters, the addr-spec is encoded inside an xtext. The syntax of an xtext is described in section 5 of [ESMTP-DSN].
Discussion:
The optional AUTH parameter to the MAIL FROM command allows cooperating agents in a trusted environment to communicate the authentication of individual messages.
If the server trusts the authenticated identity of the client to
assert that the message was originally submitted by the supplied addr-spec, then the server SHOULD supply the same addr-spec in an AUTH parameter when relaying the message to any server which supports the AUTH extension.
A MAIL FROM parameter of AUTH=<> indicates that the original submitter of the message is not known. The server MUST NOT treat the message as having been originally submitted by the client.
If the AUTH parameter to the MAIL FROM is not supplied, the client has authenticated, and the server believes the message is an original submission by the client, the server MAY supply the client's identity in the addr-spec in an AUTH parameter when relaying the message to any server which supports the AUTH extension.
If the server does not sufficiently trust the authenticated identity of the client, or if the client is not authenticated, then the server MUST behave as if the AUTH=<> parameter was supplied. The server MAY, however, write the value of the AUTH parameter to a log file.
If an AUTH=<> parameter was supplied, either explicitly or due to the requirement in the previous paragraph, then the server MUST supply the AUTH=<> parameter when relaying the message to any server which it has authenticated to using the AUTH extension.
A server MAY treat expansion of a mailing list as a new submission, setting the AUTH parameter to the mailing list address or mailing list administration address when relaying the message to list subscribers.
It is conforming for an implementation to be hard-coded to treat all clients as being insufficiently trusted. In that case, the implementation does nothing more than parse and discard syntactically valid AUTH parameters to the MAIL FROM command and supply AUTH=<> parameters to any servers to which it authenticates using the AUTH extension.
Examples:
C: MAIL FROM:<e=mc2@example.com> AUTH=e+3Dmc2@example.com
S: 250 OK
6. Error Codes
The following error codes may be used to indicate various conditions as described.
432 A password transition is needed
This response to the AUTH command indicates that the user needs to transition to the selected authentication mechanism. This typically done by authenticating once using the PLAIN authentication mechanism.
534 Authentication mechanism is too weak
This response to the AUTH command indicates that the selected authentication mechanism is weaker than server policy permits for that user.
538 Encryption required for requested authentication mechanism
This response to the AUTH command indicates that the selected authentication mechanism may only be used when the underlying SMTP connection is encrypted.
454 Temporary authentication failure
This response to the AUTH command indicates that the authentication failed due to a temporary server failure.
530 Authentication required
This response may be returned by any command other than AUTH, EHLO, HELO, NOOP, RSET, or QUIT. It indicates that server policy requires authentication in order to perform the requested action.
7. Formal Syntax
The following syntax specification uses the augmented Backus-Naur Form (BNF) notation as specified in [ABNF].
Except as noted otherwise, all alphabetic characters are case- insensitive. The use of upper or lower case characters to define token strings is for editorial clarity only. Implementations MUST accept these strings in a case-insensitive fashion.
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