I've successfully set up a forum, but even though the email settings are correct (support / bwatch.com) I'm getting my emails showing up as somethingelse@box200.bluehost.com instead. Is there any setting I missed that would prevent the email alias from working correctly?

Hmm. Apparently it's a problem that happens with a lot of scripts and I'm not able to pinpoint which plugin might have caused the problem. Anyhow, it looks like if it happens with anyone else, this plugin will fix it:

http://wordpress.org/extend/plugins/mail-from/

Thanks for your time, and for making such a wonderful product. The fact that forum post titles are also SEO'ed is very significant, and this was very much a painless installation.

PS: Spoke too soon! That plugin didn't work either. The hunt continues…

Hmm. I found the exact same problem being brought up in WordPress MU:

http://mu.wordpress.org/forums/topic.php?id=1529

I've got bluehost as well. From the post above, their solution was:

Bluehost now sent me this solution. I've tried the 'Alternative for PHP Users', without any effect. This solution implies the 'From:' header in WPMU is not formatted properly:

Problem
Why do e-mails from my webpage come from < username > @ < box > .bluehost.com when I have specified otherwise?

Solution
This is because our servers require you (or your script) to use a properly formatted, valid From: header in your email. If the From: header is not formatted correctly, empty or invalid our system will change the from address to be <username>@<box>.bluehost.com. To stop this, you must change the script you are using to correctly use a valid From header.

Examples of headers that should work would be:
From: user@domain.com
From: <user@domain.com>
From: “name” <user@domain.com>

Examples of headers that will NOT work:
From: “user@domain.com”
From: user @ domain.com

As far as I can tell, it's not a problem in the pluggable.php file either in /wp-includes/…

(I'm starting to think Bluehost is very finicky about this… also I'm not using WPMU either. Theoretically speaking, if I erased the fields in Simple Forums email settings, it should email from Wordpress@, right? But it's not even doing that…)

* Just back out of being in the hospital, The WPMU comment cought my eye *

This is from the Simple Forum FAQ - Email Issues

GENERAL Mail Issues:

Mail is not being sent.

While this general issue comes from your hosting provider’s security measures. There is a way to test what those measures may be.

The Third Party plugin WP-mail-SMTP allows you to test what e-mail address, PHPmail headers or secure SMTP setup, your hosting provider allows to send e-mail.

This multi-purpose tool is a must have for webmasters using WordPress, not just Simple Forum Users.

Oh wow, thank you very much for the plugin advice. I'll work on diagnosing it from there. And I hope everything's okay from your hospital visit.

PS:

That plugin did the trick, but not without one final tweak I found in the support forums on the plugin's site. I changed it to SMTP mail instead of PHP (though now i'm curious about swiftmail) and it turns out Bluehost's SMTP port is 26 instead of the default 25. As long as the smtp host is set to localhost:26 , then everything else works fine.

Turns out you were absolutely right in the end, sir- the whole problem I've been having in the first place was a bluehost runaround. I'm grateful for your help and continued support for this plugin. Take care!