Index: src/wp-includes/ms-functions.php
===================================================================
--- src/wp-includes/ms-functions.php	(revision 48600)
+++ src/wp-includes/ms-functions.php	(working copy)
@@ -952,7 +952,7 @@
 	$admin_email = get_site_option( 'admin_email' );
 
 	if ( '' === $admin_email ) {
-		$admin_email = 'support@' . $_SERVER['SERVER_NAME'];
+		$admin_email = 'support@' . wp_parse_url( network_home_url(), PHP_URL_HOST );
 	}
 
 	$from_name       = ( '' !== get_site_option( 'site_name' ) ) ? esc_html( get_site_option( 'site_name' ) ) : 'WordPress';
@@ -1079,7 +1079,7 @@
 	$admin_email = get_site_option( 'admin_email' );
 
 	if ( '' === $admin_email ) {
-		$admin_email = 'support@' . $_SERVER['SERVER_NAME'];
+		$admin_email = 'support@' . wp_parse_url( network_home_url(), PHP_URL_HOST );
 	}
 
 	$from_name       = ( '' !== get_site_option( 'site_name' ) ) ? esc_html( get_site_option( 'site_name' ) ) : 'WordPress';
@@ -1663,7 +1663,7 @@
 	$admin_email = get_site_option( 'admin_email' );
 
 	if ( '' === $admin_email ) {
-		$admin_email = 'support@' . $_SERVER['SERVER_NAME'];
+		$admin_email = 'support@' . wp_parse_url( network_home_url(), PHP_URL_HOST );
 	}
 
 	$from_name       = ( '' !== get_site_option( 'site_name' ) ) ? esc_html( get_site_option( 'site_name' ) ) : 'WordPress';
@@ -1755,7 +1755,7 @@
 	$admin_email = get_site_option( 'admin_email' );
 
 	if ( '' === $admin_email ) {
-		$admin_email = 'support@' . $_SERVER['SERVER_NAME'];
+		$admin_email = 'support@' . wp_parse_url( network_home_url(), PHP_URL_HOST );
 	}
 
 	$from_name       = ( '' !== get_site_option( 'site_name' ) ) ? esc_html( get_site_option( 'site_name' ) ) : 'WordPress';
Index: src/wp-includes/pluggable.php
===================================================================
--- src/wp-includes/pluggable.php	(revision 48600)
+++ src/wp-includes/pluggable.php	(working copy)
@@ -330,7 +330,7 @@
 		 */
 		if ( ! isset( $from_email ) ) {
 			// Get the site domain and get rid of www.
-			$sitename = strtolower( $_SERVER['SERVER_NAME'] );
+			$sitename = wp_parse_url( network_home_url(), PHP_URL_HOST );
 			if ( 'www.' === substr( $sitename, 0, 4 ) ) {
 				$sitename = substr( $sitename, 4 );
 			}
@@ -1650,7 +1650,7 @@
 			$notify_message .= sprintf( __( 'Spam it: %s' ), admin_url( "comment.php?action=spam&c={$comment->comment_ID}#wpbody-content" ) ) . "\r\n";
 		}
 
-		$wp_email = 'wordpress@' . preg_replace( '#^www\.#', '', strtolower( $_SERVER['SERVER_NAME'] ) );
+		$wp_email = 'wordpress@' . preg_replace( '#^www\.#', '', wp_parse_url( network_home_url(), PHP_URL_HOST ) );
 
 		if ( '' === $comment->comment_author ) {
 			$from = "From: \"$blogname\" <$wp_email>";
@@ -2831,4 +2831,3 @@
 		return $r;
 	}
 endif;
-