1) my lan uses static IP's all behind a router firewall. Internally I am 192-168.101.nnn and externally whatever the cable modem + router assigns. I use fixed addresses and IPV4 as I have a couple old Sun boxes which I don't need to upgrade with this new Linux box here. The fourth part of the address is 1 for the router and between 2 and 150 for 2 net printers, a PC, 2 suns and a Mac. I know the maximum is 255 and so everyone "internally" works and can find each other.
- so I believe everything is routable and have no problems except sendmail locally
2) I did not set a domainname (get "(none)" to `domainname` command). I could use the old one I had "rainbowapps.com" but don't see where to set it. After your original post, I did change /etc/sysconfig/network to have my hostname as rainbow.rainbowapps.com and rebooted (was localhost.localdomain), but I still get "(none)" to a domainname command. I don't see a /etc/domainname file, something which existed in Solaris and I knew to set.
I have looked at other Linux machines which are almost identical and see nothing really different. The only major difference is that these machines have a registered static IP (with godaddy) so they really do have a "legal" sendmail. I don't expect that I can use sendmail externally unless I register as static IP but I think it should work inside this local net to this host. In fact it works fine with messages showing me with a From line of "email@example.com" or firstname.lastname@example.org
depending on who sends the local mail. So this problem mail arrives to me via the local "/etc/aliases" which mails to an alias on one of the three static IP Linux boxes where it then posts again by alias to yahoo. It appears that the other box sees me as coming from com.com. I am attempting to have all my mail go one place so I don't have to read it locally and on the web. Maybe this problem is because of this other machine pass through. I cannot mail directly to yahoo as I don't have a real registered address and they would think it was spam.
Finally I am not using YP or NIS - I guess I could but don't see any good reason to do so. If you advise me to bring up NIS, I guess I could try. They both seem like overkill to me.