Index: bp-activity/bp-activity-filters.php
===================================================================
--- bp-activity/bp-activity-filters.php	(revision 3176)
+++ bp-activity/bp-activity-filters.php	(working copy)
@@ -102,7 +102,7 @@
 function bp_activity_at_name_filter( $content ) {
 	include_once( ABSPATH . WPINC . '/registration.php' );
 
-	$pattern = '/[@]+([A-Za-z0-9-_]+)/';
+	$pattern = '/[@]+([A-Za-z0-9-_\.]+)/';
 	preg_match_all( $pattern, $content, $usernames );
 
 	/* Make sure there's only one instance of each username */
Index: bp-activity/bp-activity-notifications.php
===================================================================
--- bp-activity/bp-activity-notifications.php	(revision 3176)
+++ bp-activity/bp-activity-notifications.php	(working copy)
@@ -4,7 +4,7 @@
 	global $bp;
 
 	/* Scan for @username strings in an activity update. Notify each user. */
-	$pattern = '/[@]+([A-Za-z0-9-_]+)/';
+	$pattern = '/[@]+([A-Za-z0-9-_\.]+)/';
 	preg_match_all( $pattern, $content, $usernames );
 
 	/* Make sure there's only one instance of each username */
Index: bp-groups/bp-groups-notifications.php
===================================================================
--- bp-groups/bp-groups-notifications.php	(revision 3176)
+++ bp-groups/bp-groups-notifications.php	(working copy)
@@ -240,7 +240,7 @@
 	global $bp;
 
 	/* Scan for @username strings in an activity update. Notify each user. */
-	$pattern = '/[@]+([A-Za-z0-9-_]+)/';
+	$pattern = '/[@]+([A-Za-z0-9-_\.]+)/';
 	preg_match_all( $pattern, $content, $usernames );
 
 	/* Make sure there's only one instance of each username */