I would like a form that allows visitors to check the availability of a desired email ID (single custom field) before they place an order. So, for example, visitor #1 types in "johnsmith" into the EMAILID field. The form accepts the submission as valid since no other visitor has reserved "johnsmith." Then, if visitor #2 comes along and enters "johnsmith" into the EMAILID field, he will get a message stating that "the EMAILID 'johnsmith' name is already reserved, try another."
This is similar in function to checking the whois for domain names, except that all the names are stored in "EMAILID" field of form submission table not any external server, which continues to grow as users submit unique EMAILIDs.
Can someone give me a lead on how I can set this up with GravityForms?