Index: src/wp-includes/pluggable.php
===================================================================
--- src/wp-includes/pluggable.php	(revision 28222)
+++ src/wp-includes/pluggable.php	(working copy)
@@ -344,12 +344,17 @@
 	 */
 
 	if ( !isset( $from_email ) ) {
-		// Get the site domain and get rid of www.
-		$sitename = strtolower( $_SERVER['SERVER_NAME'] );
-		if ( substr( $sitename, 0, 4 ) == 'www.' ) {
-			$sitename = substr( $sitename, 4 );
+		//Get the site domain.
+		$sitename = parse_url( get_bloginfo("wpurl"), PHP_URL_HOST );
+
+		//Strip any subdomains to ensure we're using wp@domain.tld.
+		$chunks = explode(".", $sitename);
+		$chunkscount = count($chunks);
+		if ( $chunkscount >= 3 ) {
+			//Only use the primary domain and TLD.
+			$sitename = $chunks[$chunkscount -2] . "." . $chunks[$chunkscount -1];
 		}
-
+		
 		$from_email = 'wordpress@' . $sitename;
 	}