I.E.C.C. Bulk Mail Transfer Protocol (BMTP) provides a channel for the delivery of ''bulk mail'' electronic mail. BMTP is a service parallel to but sepa- rate from SMTP. The specification of BMTP is intended to be similar enough to SMTP that existing SMTP clients and servers can easily be adapted for BMTP. Extensions provide for categorizing messages by class, and for authorizing the client to the server, to aid in the implementation of cost-sharing systems.