Here's a fairly simple technique to do what you want with only minor modifications to your mod_perl code: create a mod_perl cleanup handler that will check for any unsent messages in the database and send them. Make it loop until there are none left. This will mean that whenever messages come in, all of the processes that took the messages will stick around to send messages until the queue is cleaned out. The only danger of this approach is that you could end up tying up all of your processes sending messages and leave none to receive. To get around this, you could keep track of how many processes are in "send mode" at any given time, and have new processes skip the sending step if too many are already doing it. That may be unnecessary though.

The advantage of using apache (via mod_perl) as your daemon is that it's fast, stable, secure, handles SSL, has flexible logging, speaks HTTP, etc. Don't switch to something else without a really good reason.

If you need really great performance (it doesn't sound like you do), you would probably want to use some kind of single process non-blocking I/O approach, since most of the work is just waiting for I/O to complete. You could look at POE, although I'm not sure how well it performs under load.