jQuery Validate Plugin - Trigger validation of single field
Solution 1:
This method seems to do what you want:
$('#email-field-only').valid();
Edit
API has changed, see Paul's answer.
Solution 2:
Use Validator.element():
Validates a single element, returns true if it is valid, false otherwise.
Here is the example shown in the API:
var validator = $( "#myform" ).validate();
validator.element( "#myselect" );
.valid() validates the entire form, as others have pointed out. The API says:
Checks whether the selected form is valid or whether all selected elements are valid.