>   1. My 3com 3c905b (vortex) isn't coming up in 100MB mode.

Sorry, no clue on that one.

>   2. My mail server doesn't seem to be getting mail from Yahoo or AOL
> (possibly others). All mail sent from these servers gets returned. The
> domain is registered through Network Solutions and has been for some time
> (several months). How do I make these people recognize my
> address? A simple
> lookup reveals the address of the website, and the name servers. Querying
> the name servers returns the mail server address? What gives?

Check /var/log/messages and whatnot and see if the mail server is getting
contacted but rebuffing Yahoo's advances like a cocky silicon valley startup
drunk on VC.

I see this kind of black-hole behavior a lot when DNS has gotten screwy.  If
you had your domain parked someplace previously, you may need to tell them
to stop being authoritative for the domain.  A little time with 'dig' and a
list of IPs that have ever been nameservers for your domain might do the
trick.  ('dig @123.123.123.123 hostname.com' will do a DNS lookup for
'hostname.com' using the DNS server 123.123.123.123, so you can check to be
sure formerly-authoritative servers are delegating properly.)

Also see the awesome tools at:  http://www.geektools.com/  Their traceroute
links and whois queries are very handy for this kind of thing.

Of course, the best thing to do is a 'mail -v' on one of the hosts having
trouble mailing you, but that's seldom possible.

-glenn