Here is what my problem was:
1. Guests using hotmail or yahoo mail as their primary e-mail would never get a "activation" e-mail. There are surely other e-mail systems that also have this problem but I don't know.
2. Guests trying to register with an IP based e-mail for the registration process did not have problems getting through the full registration process.
3. I was using a "gmail" e-mail address for the "Admin Mail Address" found in the XOOPS Admin Control Panel at Preferences Main »» General Settings Why this happends?
Hotmail and Yahoo Mail thought the automated "activation e-mail" that XOOPS sends out was sp*m or some kind of IP spoofing. These e-mails never reach their intended destination In-Box as they were blocked right at the Hotmail/Yahoo server.The Fix:
I changed the site "Admin Mail Address" to an email that matched my website IP. For example:
Old "Admin Mail Address": firstname.lastname@example.org
New "Admin Mail Address": email@example.com
Hopefully someone out there will find this fix useful.
Transferred from forums with thanks toTopKnot