From this blog post:

rss2email randomly goes unconditional at times. No idea why.

We actually behave nicely:

• We make a first request to each feed, as we run.
• We save any cache-headers.
• The next time we poll the feed(s) we use the appropriate cache-headers.

Can you see where this is going? Yes, we don't persist the headers. So:

• User launches the deamon.
• All feeds are polled, once, unconditionally.
• User restarts the daemon.
• All feeds are polled, once, unconditionally.

We should save/load the cache values. This will also ensure we're good for the one-shot cron-based runs, not just the persistant daemon-based runs.