This is a port of an addon I made for vBulletin back in September of 2014
The settings for the mod can be found under, [OzzModz] Block Registrations With Spam Like Email Addresses

Note: The error message they see when they exceed the maximum dots is this:

"The administrator has blocked the email you have entered for containing to many special characters. Please try a different email address."
I would not suggest changing it and saying something like, " you entered to many dots " or some such as this will just tip the spammers off.

Complete Feature List

• Option to disable the mod completely.
• Option to set the maximum dots allowed. ( ala . ) I suggest no more than two dots allowed.
• Option to set the maximum pluses allowed. ( ala + ) I suggest no more than 1 plus allowed.
• Option to set the maximum hyphens allowed. ( ala - ) I suggest no more than 1 hyphen allowed.
• Option to set the maximum underscores allowed. ( ala _ ) I suggest no more than 1 underscore allowed.
• Option to set the maximum tildes allowed. ( ala ~ ) I suggest no more than one tilde allowed.

Frequently Asked Questions.

Q. Why do I need such a thing, you ask?
A. I have seen a rash of users joining sites, with multi dotted or multi special characters email addresses, and 99.9% of the time these are spammers, usually human ones. So by adding this you can prevent them from registering.