I was just curious but I recently wanted to email everyone from my forum by extracting all the addresses from the database only to find out that 25% of the addresses were fake. Is there a way that miniBB could validate the addresses using checkdnsrr() and only let them register with a valid address without using email activation of course. Just a thought and think it would be a neat feature.

Valid DNS doesn't mean obligately there will be a valid email address on it. For example, minibb.com is a valid domain, but there is no email kkdsd08h [on] minibb.com which could be still used in registration.

I think if you would like to get all valid emails, there is no other way than to validate it upon registration setting up the option $closeRegister.