Replacement for Sendmail

Hi What would be a good replacement for Sendmail? I have linux-router with fetchmail / sendmail running, and both win and Linux "clients" on LAN-side. There is ADSL-line out from it. Fetchmail-side is working nicely. Now I have found Sendmail to be really out-of-date what comes to configuration. I can't get it to work, it just gives "realying denied" no matter what I try. I have been able to set it so, that every domain-name I manually code into the configuration is accepted, but surely there must be some "*" somewhere, but it just won't work, and docs are of no use. So it is out-of-date piece of SW. So, I need to replace it with a modern package. Jaska.