I want web interfaces to send to any address via SMTP, but when I do it through 127.0.0.1 port 25, exim complains that I'm relaying. I'm running Debian testing, and /etc/exim/exim.conf is empty. To just let outgoing mail work -- only from 127.0.0.1, not as an open relay -- is there a quick configuration line I can put in there?

Found my own answer on my debian laptop:

# The setting below allows your host to be used as a mail relay only by
# localhost: it locks out the use of your host as a mail relay by any
# other host. See the section of the manual entitled "Control of relaying"
# for more info.

host_accept_relay = 127.0.0.1 : ::::1