Mailbox unavailable. The server response was: No such user here

i have been successfully sending email from web page for many weeks since i deployed my website
these days i get the error message :Mailbox unavailable. The server response was: No such user here
when i tried to send email to friends or even to my hotmail account.. the only change i made in my website is to play media could this be the reason!
<STYLE type=text/css>
.ctl00_main_0 { background-color:white;visibility:hidden;display:none;position:absolute;left:0px;top:0px; }
.ctl00_main_1 { text-decoration:none; }
.ctl00_main_2 { width:100%; }