Change hamburger icon to envelope mail icon in main menu .

Add this into the Custom CSS box located in your Salient Options panel (Make Sure there are no red cross in the Box) :

#header-outer.transparent header#top nav ul .slide-out-widget-area-toggle a i.lines-button.x2:after {
    content: "\f0e0";
    position: absolute;
    font-family: FontAwesome;
    font-size: 20px !important;
    line-height: 24px !important;
    font-style: normal;
}
#header-outer.transparent header#top nav ul .slide-out-widget-area-toggle a i.lines {
    display: none !important;
}
header#top .span_9 > .slide-out-widget-area-toggle i:before {
    content: "\f0e0" !important;
    position: absolute;
    font-family: FontAwesome;
    font-size: 20px !important;
    line-height: 24px !important;
    font-style: normal;
}
#header-outer[data-full-width="true"] .slide-out-widget-area-toggle .open > span {
    -webkit-transform: none !important;
    transform: none !important;
}