RFC 1870 (rfc1870) - Page 2 of 9

SMTP Service Extension for Message Size Declaration

RFC 1870                 SMTP Size Declaration             November 1995


3.  Framework for the Size Declaration Extension

   The following service extension is therefore defined:

   (1) the name of the SMTP service extension is "Message Size
       Declaration";

   (2) the EHLO keyword value associated with this extension is "SIZE";

   (3) one optional parameter is allowed with this EHLO keyword value, a
       decimal number indicating the fixed maximum message size in bytes
       that the server will accept.  The syntax of the parameter is as
       follows, using the augmented BNF notation of [2]:

           size-param ::= [1*DIGIT]

       A parameter value of 0 (zero) indicates that no fixed maximum
       message size is in force.  If the parameter is omitted no
       information is conveyed about the server's fixed maximum message
       size;

   (4) one optional parameter using the keyword "SIZE" is added to the
       MAIL FROM command.  The value associated with this parameter is a
       decimal number indicating the size of the message that is to be
       transmitted.  The syntax of the value is as follows, using the
       augmented BNF notation of [2]:

           size-value ::= 1*20DIGIT

   (5) the maximum length of a MAIL FROM command line is increased by 26
       characters by the possible addition of the SIZE keyword and
       value;

   (6) no additional SMTP verbs are defined by this extension.

   The remainder of this memo specifies how support for the extension
   affects the behavior of an SMTP client and server.

4.  The Message Size Declaration service extension

   An SMTP server may have a fixed upper limit on message size.  Any
   attempt by a client to transfer a message which is larger than this
   fixed upper limit will fail.  In addition, a server normally has
   limited space with which to store incoming messages.  Transfer of a
   message may therefore also fail due to a lack of storage space, but
   might succeed at a later time.





Klensin, et al              Standards Track