I'd like to thank everybody who took the trouble to respond.
The overwhelming endorsement is for Exim:
ftp://ftp.cus.cam.ac.uk/pub/software/programs/exim/exim-n.nn.tar.gz
This is already in use at Cambridge, Imperial, Strathclyde amongst others
and is to be the recommended MTA shipped on the next GNU cdrom.
Also mentioned as in use at a couple of sites were smail and qmail.
Messageware is indeed Nexors new name for what was PP. Also mentioned
was the source version of PP available from the ISODE consortium.
I hope the above is as useful.
Tony
--------------------------------------------------------
Tony Povoas email: tony@???
Systems Manager phone: +34 22 42 5447
Sea Level Office fax: +34 22 42 5401
Isaac Newton Group
Observatorio del Roque de la Muchachos
La Palma
Canary Islands