I'm delighted to advise that, for new Clients that haven't had their domain email address/es in the public domain, my Spam Block Email Extension, combined with the additional email form validation is working beautifully, with no spam received.
However, I do have other Clients that had their email address in the public domain, including website before my Spam Blocking Email Extension and have found that a large volume of spam is being sent from spoofed email addresses.
For those of you unaware, spoofed email addresses are where a sender masks their sent email address as opposed to their actual (reply to) email address. For example - actual address - pita@gmail.com - sent email address - bovineexcrement@firstpageongoogle.com.
The email address pita@gmail.com doesn't actually exist, so blocking this sender in your email delivery Client or adding it to a spam blacklist will have no effect on stopping the actual email address.
Of course the big pain with gmail is that you can block one email address, and it's so easy for the spammer to then just create another gmail address.
With legitimate email addresses from a specific domain you could blacklist the domain. But, because so many people use gmail that is risky.
So I did some digging and found this :
I would like to report a Gmail user who has sent messages that violate the Gmail Program Policies and/or Terms of Use.
Disclaimer - I have absolutely no idea whether it will do any good and if Gmail (Google) even care about gmail users spamming.
Thought I'd share it anyway. At the risk of being a Utopian Optimist
, hopefully if enough people use it Gmail (Google) will develop a conscience - I live in hope! 
