send mail to multiple receiver with HTML mailto [duplicate]
"There are no safe means of assigning multiple recipients to a single mailto: link via HTML. There are safe, non-HTML, ways of assigning multiple recipients from a mailto: link."
http://www.sightspecific.com/~mosh/www_faq/multrec.html
For a quick fix to your problem, change your ; to a comma , and eliminate the spaces between email addresses
<a href='mailto:[email protected],[email protected]'>Email Us</a>