I've never worked with sendmail before, so I've just been playing around with different settings. This is what I have so far:
I have steve.local (machine's internal domain) marsonist.servehttp.com and localhost listed as internal domains--- without marsonist.servehttp.com listed I wasn't able to forward local user traffic with that domain. It would just be stuck in queue.
I have my domain masquerading and outgoing domains setup so that all mail comes from marsonist.servehttp.com
I also have my spam control to allow mail from the above domain.
I've been using webmin to set it up. Maybe that's a mistake, but as a first time user of sendmail I thought it might help.
no-ip.com asks for an mx address to send the mail to, but I'm not sure what that is either.
Thanks for your quick response.