dig alum.mit.edu mx
works fine, but I get "unrouteable mail domain" errors from exim anyway. What causes this kind of problem?

Once again I found the answer on my own laptop. The top of my exim.conf says
# This is the main exim configuration file.
# It was originally generated by `eximconfig', part of the exim package

I don't remember having to run eximconf by hand before. For some reason, either initially or after upgrading to Debian testing, my linode had an empty exim.conf. All better now.

I wonder what config utility didn't run that explains why localhost doesn't resolve to 127.0.0.1 for me?

Does /etc/hosts exist?

If not:

echo "127.0.0.1 localhost" > /etc/hosts

-Chris

What's strange is it did exist, including some ip6 entries added by a netbase upgrade. I added the localhost entry manually as you suggested.

I had difficulty with mail on my linode. Asked Google.
Google told me to look at this thread.

Maybe I'll come here first next time.


One more step in the above thread....
/etc/init.d/exim start

(I know it's a no-brainer, but it makes the thread complete