But at the same you're using the Visual CAPTCHA Plugins as anti-spam measure that have been long broken by the spambotsRegistration using a gmail.com address has been blocked due to massive amount of spambots registering through gmail. Please use an email address from a private or for-pay email hoster instead.
see the article on phpBB.com
https://www.phpbb.com/community/viewtop ... &t=2122696
So, simply change captcha to prevent spam, a Q&A challenge will do the trick! no need to block gmailBroken Visual CAPTCHA Plugins
These CAPTCHAs are included in the stock install but have been broken by spambots. They are ineffective and should not be used.