Berkeley Mail was (according to def.h) developed by Kurt Shoens, dated
March 25, 1978. I very much regret that it seems impossible to include
the people that contributed within the around fifteen years of history
of BSD Mail. If you know more about this, contact me.

After the 4.4BSD release in 1993, Mail was not further developed officially.
The code that nail is based on contains numerous patches from OpenBSD, NetBSD,
RedHat and Debian. Namely the NetBSD developer Christos Zoulas wrote much
of it.

The maintainer and primary developer of nail is Gunnar Ritter. Nail
development started in February 2000 and especially the MIME code,
network protocol support, and POSIX conformance improvements.

See the ChangeLog for people who have contributed to nail.