(nb "<", ">" and "\n"s are stripped)
In case (some of) these environment variables are not set, the information
is taken from the configuration items user.name and user.email, or, if not
-present, system user name and the hostname used for outgoing mail (taken
+present, the environment variable EMAIL, or, if that is not set,
+system user name and the hostname used for outgoing mail (taken
from `/etc/mailname` and falling back to the fully qualified hostname when
that file does not exist).