This chapter describes how to tunnel messages between two or more cooperating PMDF systems using Batch SMTP (BSMTP). In addition, use of PMDF's general conversion facilities to provide services such as payload compression and digital signatures for authentication and integrity is described.

Batch SMTP (BSMTP) is a batch-mode implementation of the SMTP protocol which turns SMTP into a remote-submission protocol. For over a decade, batch SMTP was used quite heavily as a message transfer protocol on the international BITNET network. Cooperating PMDF sites can use BSMTP as an effective means of moving mail in bulk between one another; for instance the exchange of company e-mail between two company offices by means of the Internet.

With BSMTP, messages are bundled together on one PMDF system and then periodically transmitted through arbitrary MTAs and networks to a remote PMDF system. Upon receipt at the remote system, the bundle is unpacked and the individual messages sent on to their recipients. With PMDF's general conversion facilities, arbitrary transformations can be performed on the bundles such as document conversion, compression, addition of digital signatures for authentication and integrity, etc. This chapter provides examples of compression using the Free Software Foundation's GZIP and GUNZIP utilities and authentication using Pretty Good Privacy, Inc.'s PGP® utility.¹