Request for assistance

[Mark Glassberg]

Pardon my ignorance--I'm an advanced newbie.  I've telneted to my mail
server and sent messages.  The messages which my sendmail has bounced
indicate that the server is unable to get my machine's hostname.  I
experimented with telnet using many names (including a dot) after HELO
and was recognized, but was rejected whenever the name had an @ in it.
I strongly suspect that my sendmail is trying to use localmailer at localhost
to contact the server.  Do you know how I can edit sendmail.cf to stop
using a @ in the HELO line?

Thanks in advance,
Mark

P.S.:  I'm obviously using another isp to send this.