LinuxQuestions.org - Problems getting sendmail to work how I want it to

So I just finished installing/configuring sendmail a few days ago, and for some reason, I still can't get it to do what I want.

What's Right:

When a user sends an e-mail to my account, webmaster@thegreggor.com, I receive it perfectly, and can then read it in Mutt.

When I send an e-mail to an address, it is received intact as well.

What's Wrong:

When the e-mail reaches its destination, it is marked as coming from root@gregroute.thegreggor.com, NOT root@thegreggor.com. This means that when the person tries to reply, it sends it to root@gregroute.thegreggor.com, and thus the e-mail request is denied due to unknown domain. I know there are several work-arounds for this. I could just set up a subdomain called gregroute.thegreggor.com. I could also use telnet to send the e-mail manually from webmaster@thegreggor.com or root@thegreggor.com (both of these methods worked when I tried them). But the point is that I want to be able to send out of a normal e-mail client without having to hassle around with these issues. What makes sendmail default to user@host.domain.com rather than user@domain.com and how do I stop it?

The other issue is that, try as I may, I cannot send e-mails from another box, even one on my LAN. It said something about relaying denied, I think. I don't remember the exact error, but I'll post it up when I get home. POP3 has not yet been set up on the box hosting sendmail, but I'll get that up and running later. I was using thunderbird on a Windows XP Pro computer.

Also, one more thing that's kind of bothersome but not really critical is that when someone sends a message to webmaster, it automatically reaches root's mailbox. Furthermore, when I try to open up Mutt on webmaster's account, it says that "/home/webmaster/.maildir mailbox does not exist". It would be nice if root and webmaster had separate mail accounts so that I don't have to log root in everytime to check my mail.

Finally, if anyone has any insight into MTA operation, would it honestly be better for a newer linux user to adopt a simpler MTA like Qmail than bother with Sendmail? Or would it be more of a hassle to reconfigure everything and get used to it?

Any help would be appreciated. If you need any extra information that I haven't provided, please ask.

Thanks in advance,

Greggor

EDIT: Ah, I should mention before I get flamed that I did try googling it, searching the (imo) poor sendmail documentation, and checking the man pages for solutions to all of these problems... I found, unfortunately, that I couldn't find what I was looking for. Either I just don't know what to search or no one has run into a similar problem :\