This memo defines two new service extensions to the SMTP service. The first service enables a SMTP server to indicate the maximum size RFC822 header it is willing to accept in a message. The second enables a SMTP client and server to negotiate the use of 8bit or or 8bit encoded binary contents within the message header. This memo specifies the algorithms necessary for the interworking between extended clients with a large and binary header and non-extended SMTP servers. It is expected this document may be split into three, 1) The ESMTP messageheader SIZE extension, 2) the ESMTP 8bit message header encoding extension, and 3) the registration of the