【文章內(nèi)容簡(jiǎn)介】 :The optional AUTH parameter to the MAIL FROM mand allows cooperating agents in a trusted environment to municate the authentication of individual messages.If the server trusts the authenticated identity of the client toAssert that the message was originally submitted by the supplied addrspec, and then the server SHOULD supply the same addrspec 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 client39。s identity in the addrspec 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 hardcoded 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 mand and supply AUTH= parameters to any servers to which it authenticates using the AUTH extension.Examples:C: MAIL FROM : e=mc2@ AUTH=e+3Dmc2@S: 250 OK6. Error CodesThe following error codes may be used to indicate various conditions as described.432 A password transition is neededThis response to the AUTH mand indicates that the user needs to transition to the selected authentication mechanism. This typically done by authenticating that once using the PLAIN authentication Authentication mechanisms is too weak.This response to the AUTH mand indicates that the selected authentication mechanism is weaker than server policy permits for that user.538 Encryption required for requested authentication mechanismThis response to the AUTH mand indicates that the selected authentication mechanism may only be used when the underlying SMTP connection is encrypted.454 Temporary authentication failuresThis response to the AUTH mand indicates that the authentication failed due to a temporary server failure.530 Authentication requiredThis response may be returned by any mand 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 SyntaxThe following syntax specification uses the augmented BackusNaur 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 caseinsensitive fashion.8. Security ConsiderationsSecurity issues are discussed throughout this memo. If a client uses this extension to get an encrypted tunnel through an insecure network to a cooperating server, it needs to be configured to never send mail to that server when the connection is not mutually authenticated and encrypted. Otherwise, an attacker could steal the client39。s mail by hijacking the SMTP connection and either pretending the server does not support the Authentication extension or causing all AUTH mands to fail.Before the SASL negotiation has begun, any protocol interactions are performed in the clear and may be modified by an active attacker. For this reason, clients and servers MUST discard any knowledge obtained prior to the start of the SASL negotiation upon pletion of a SASL negotiation which results in a security layer.This mechanism does not protect the TCP port, so an active attacker may redirect a relay connection attempt to the submission port [SUBMIT]. The AUTH= parameter prevents such an attack from causing a relayed message without an envelope authentication to pick up the authentication of the relay client.A message submission client may require the user to authenticate whenever a suitable SASL mechanism is adve