Update: So, today I got to the heart of the problem and fixed it.
We have noticed something odd happening to our forum over the past few months: our registration numbers have been dwindling. At first, we weren't able to understand why, but as new members started PM'ing the staff and emailing me, we figured out that people weren't getting our confirmation emails. I have tried several different fixes, but none of them would work. Today I found the cause and fixed the problem.
For years ClubSX4 had used Yahoo mail as our primary mail distributor. A few months back, Yahoo quietly activated a parameter in their email distribution software which stopped allowing third parties from sending emails through Yahoo's servers. This significantly cut down on the spam that was being sent through Yahoo's servers, but also made it impossible for the thousands of legitimate businesses, clubs, groups, organizations, nonprofits and forums who relied on this service to send out these emails from getting through. (For more info on this, please Google: Yahoo DMARC)
The permanent fix for us was to get off of Yahoo's email servers and use my own server that this forum is hosted on.
The benefit of using Yahoo was that Yahoo is a strong email server that is consistent. It also has excellent spam filters. I'm going to lose some of the usability that comes with a big service like that (I have read reports saying most large email companies will likely implement the DMARC, so just changing over to another one wouldn't guarantee this couldn't happen again) but hosting the email on my own server will mean I'll stay more in control of my own distribution.
The link and information in the first post still applies, if you have registered and not received your confirmation email, try that link. If it still doesn't work, PM or email me (Using the Contact Us link on the bottom of ever page on the forum) and I will help you get signed up.
The path to heaven runs through miles of clouded hell.