RFC 1893 - SMTP Extended Error MessagesImage

   For more detail about the RFC1893 : http://www.faqs.org/rfcs/rfc1893.html

   The class sub-code provides a broad classification of the status.
   The enumerated values the class are defined as:

    2.X.X   Success

       Success specifies that the DSN is reporting a positive delivery
       action.  Detail sub-codes may provide notification of
       transformations required for delivery.

    4.X.X   Persistent Transient Failure

       A persistent transient failure is one in which the message as
       sent is valid, but some temporary event prevents the successful
       sending of the message.  Sending in the future may be successful.

    5.X.X   Permanent Failure

       A permanent failure is one which is not likely to be resolved by
       resending the message in the current form.  Some change to the
       message or the destination must be made for successful delivery.

       X.0.X   Other or Undefined Status

          There is no additional subject information available.

       X.1.X   Addressing Status

          The address status reports on the originator or destination
          address.  It may include address syntax or validity.  These
          errors can generally be corrected by the sender and retried.

       X.2.X   Mailbox Status

          Mailbox status indicates that something having to do with the
          mailbox has cause this DSN.  Mailbox issues are assumed to be
          under the general control of the recipient.

       X.3.X   Mail System Status

          Mail system status indicates that something having to do
          with the destination system has caused this DSN.  System
          issues are assumed to be under the general control of the
          destination system administrator.

       X.4.X   Network and Routing Status

          The networking or routing codes report status about the
          delivery system itself.  These system components include any
          necessary infrastructure such as directory and routing
          services.  Network issues are assumed to be under the
          control of the destination or intermediate system

       X.5.X   Mail Delivery Protocol Status

          The mail delivery protocol status codes report failures
          involving the message delivery protocol.  These failures
          include the full range of problems resulting from
          implementation errors or an unreliable connection.  Mail
          delivery protocol issues may be controlled by many parties
          including the originating system, destination system, or
          intermediate system administrators.

       X.6.X   Message Content or Media Status

          The message content or media status codes report failures
          involving the content of the message.  These codes report
          failures due to translation, transcoding, or otherwise
          unsupported message media.  Message content or media issues
          are under the control of both the sender and the receiver,
          both of whom must support a common set of supported

       X.7.X   Security or Policy Status

          The security or policy status codes report failures
          involving policies such as per-recipient or per-host
          filtering and cryptographic operations.  Security and policy
          status issues are assumed to be under the control of either
          or both the sender and recipient.  Both the sender and
          recipient must permit the exchange of messages and arrange
          the exchange of necessary keys and certificates for
          cryptographic operations.

       X.0.0     Other undefined Status

          Other undefined status is the only undefined error code. It
          should be used for all errors for which only the class of the
          error is known.

       X.1.0     Other address status
       X.1.1     Bad destination mailbox address
       X.1.2     Bad destination system address
       X.1.3     Bad destination mailbox address syntax
       X.1.4     Destination mailbox address ambiguous
       X.1.5     Destination mailbox address valid
       X.1.6     Mailbox has moved
       X.1.7     Bad sender's mailbox address syntax
       X.1.8     Bad sender's system address

       X.2.0     Other or undefined mailbox status
       X.2.1     Mailbox disabled, not accepting messages
       X.2.2     Mailbox full
       X.2.3     Message length exceeds administrative limit.
       X.2.4     Mailing list expansion problem

       X.3.0     Other or undefined mail system status
       X.3.1     Mail system full
       X.3.2     System not accepting network messages
       X.3.3     System not capable of selected features
       X.3.4     Message too big for system

       X.4.0     Other or undefined network or routing status
       X.4.1     No answer from host
       X.4.2     Bad connection
       X.4.3     Routing server failure
       X.4.4     Unable to route
       X.4.5     Network congestion
       X.4.6     Routing loop detected
       X.4.7     Delivery time expired

       X.5.0     Other or undefined protocol status
       X.5.1     Invalid command
       X.5.2     Syntax error
       X.5.3     Too many recipients
       X.5.4     Invalid command arguments
       X.5.5     Wrong protocol version

       X.6.0     Other or undefined media error
       X.6.1     Media not supported
       X.6.2     Conversion required and prohibited
       X.6.3     Conversion required but not supported
       X.6.4     Conversion with loss performed
       X.6.5     Conversion failed

       X.7.0     Other or undefined security status
       X.7.1     Delivery not authorized, message refused
       X.7.2     Mailing list expansion prohibited
       X.7.3     Security conversion required but not possible
       X.7.4     Security features not supported
       X.7.5     Cryptographic failure
       X.7.6     Cryptographic algorithm not supported
       X.7.7     Message integrity failure


For more detail about the RFC788 : http://www.faqs.org/rfcs/rfc788.html

=> List of reply codes returned by destination server when source server is sending a command during SMTP session.

211   System status, or system help reply
214   Help message  [Information on how to use the receiver or the meaning of a particular non-standard command; this reply is useful only to the human user]
220   Service ready
221   Service closing transmission channel
250   Requested mail action okay, completed
251   User not local; will forward to

354   Start mail input; end with .

421   Service not available, closing transmission channel [This may be a reply to any command if the service knows it must shut down]
450   Requested mail action not taken: mailbox unavailable [E.g., mailbox busy]
451   Requested action aborted: local error in processing
452   Requested action not taken: insufficient system storage

500   Syntax error, command unrecognized [This may include errors such as command line too long]
501   Syntax error in parameters or arguments
502   Command not implemented
503   Bad sequence of commands
504   Command parameter not implemented
550   Requested action not taken: mailbox unavailable [E.g., mailbox not found, no access]
551   User not local; please try
552   Requested mail action aborted: exceeded storage allocation
553   Requested action not taken: mailbox name not allowed [E.g., mailbox syntax incorrect]
554   Transaction failed