After a quick research here and here, the solutions didn't work for my project.
Here is the regex:
"^([A-Za-z0-9\._%-]+@[A-Za-z0-9\.-]+\.[A-Za-z]{2,4}+[;]?)(?:[;][A-Za-z0-9\._%-]+@[A-Za-z0-9\.-]+\.[A-Za-z]{2,4}+[;]?)*$|^$"
And here is an error that firebug fires at me whenever I reach email validation step (see regex above):
invalid quantifier hasformat()jquery...tion.js (line 211) pattern = "\^([A-Za-z0-9\._%-]+@[A...-Za-z]{2,4}+[;]?)*$|^$\"