set from: address in standard command-line mailer (/usr/bin/mail)

[Miles Bader <miles.bader@necel.com>]

When I send mail using /usr/bin/mail, the From: address is wrong; it's
apparently just prepending my user-id to my domainname.

How can I tell mail to use a different From: address?  I've trawled
through the docs, but not found an answer... [the docs are pretty weird
to tell the truth -- they're a flashback to about 1983, and make it
sound like network email is something of a novelty.]

Thanks,

-miles
-- 
`...the Soviet Union was sliding in to an economic collapse so comprehensive
 that in the end its factories produced not goods but bads: finished products
 less valuable than the raw materials they were made from.'  [The Economist]