If sendmail scares you, use qmail. Qmail is extremely secure, robust, and stable. Relaying via qmail is simple too (just edit the /etc/tcp.smtp file and allow machines or subnets to relay).

Is there some compelling reason that you wish to avoid using your ISP's server? If not, I'd just set up the smarthost for all outgoing mail and be done with it. It will save you many a headache as ...