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Do you mean blocking a particular IP from submitting the form? Unfortunately, banning or blocking of IP address is not doable in the form builder. You cannot create condition logic for this since IP addresses are only checked/recorded after submission process.
Instead you can by create a hide condition rule on a particular email address, just set it in that If the E-mail is entered then hide: Submit button.
The easier way to do it is on your web server. You can blacklist IPs that goes to your website/domain where the form is embedded.
Do let us know if this addresses the issue you were reffering to, looking forward to serving you further.
I am refering to blocking specific senders from posting spam messages via Jotform and enclose a copy of what I mean:
NameJessica Grahame-mail firstname.lastname@example.orgQuery or commentI volunteer some of my time to help nonprofits with their websites. I worked in IT for 23 years and was a professional webmaster too. I've helped eight organizations so far. Do you have any interest in getting a new website for free? I just helped an animal shelter and their site is really nice now. I helped a women's center before that. Sincerely, Jessica Graham
This person (Jessica Graham) is based in the Philippines and wants your FTP details to turn your website into a bot. Obviously I do not want her to be able to post mails on my forms; how do I block her from doing this?
You can limit the number of submittions,use captcha or unique submittions.This can be done by following this link http://www.jotform.com/help/64-How-to-Set-Unique-Submissions-on-a-Form.
I hope that works for you.
Unfortunately, it is not possible to block some senders. We have prevention against automated spam. But, this is obviously filled manually by a person.