tlug: Not acceptable to SMTP server

[Dave Gutteridge <dave@example.com>]

First before I say anything else, I just wanted to publicly say thanks to
Daniel and his Linux Guru friends, my Linux server is up and running again.
(Yay!!). After months of me banging my head against this thing, these guys
had me straightened out in mere hours.

So it's working, and so now I can hopefully learn Linux and server issues
without stressing out.
The first question:
I'd like to set up one e-mail account, called "dave@example.com". Daniel has
set it up for me so far in that I can recieve mail via that account. When I
try to send mail, however, it says "The recipient [in here is anyone i try
to e-mail] is not acceptable to your SMTP server. The mail can not be
delivered until the recipient is changed". 
I can't imagine that there has been a security setting to deny certain
recipients, so why would the recipient be invalid?
Perhaps this is related: Mail that comes to me is labelled "X-POP3-Rcpt:
dave@example.com". Is this significant? I know the machine name is dserver, but
shouldn't that be replaced by sendmail to read "dave@example.com"?



However, when the mail arrives to me, it comes to me saying that it is
addressed to dave@example.com, or at least it says this:
X-POP3-Rcpt: dave@example.com 
Hmmm... the machine name is dserver, so it's not a mystery where the name
came from. But i don't understand why if the mail can find me, why it has a
different address.
And, possibly connected to that



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