I second, what moritz said. It's even better to let an external mechanism watch over your process (e.g Solaris Service Management Facility or the Daemon::-Modules from CPAN).

However, if you insist to follow that path, the following entries from the FAQ should point you in the right direction to implement your own appender:

• How can I configure Log::Log4perl to send me email if something happens?
• How can I write my own appender?

Studying Log::Log4perl::Filter might be useful too.

HTH