Index: bp-activity/bp-activity-functions.php
===================================================================
--- bp-activity/bp-activity-functions.php	(revision 4042)
+++ bp-activity/bp-activity-functions.php	(working copy)
@@ -19,7 +19,7 @@
  * @return array $usernames Array of the found usernames that match existing users
  */
 function bp_activity_find_mentions( $content ) {
-	$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 4042)
+++ bp-activity/bp-activity-notifications.php	(working copy)
@@ -12,7 +12,7 @@
 	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-forums/bp-forums-filters.php
===================================================================
--- bp-forums/bp-forums-filters.php	(revision 4042)
+++ bp-forums/bp-forums-filters.php	(working copy)
@@ -123,7 +123,7 @@
 
 	$content = htmlspecialchars_decode( $content );
 
-	$pattern = "|<a href=&#039;" . bp_get_root_domain() . "/" . $bp->members->slug . "/[A-Za-z0-9-_\.]+/&#039; rel=&#039;nofollow&#039;>(@[A-Za-z0-9-_\.]+)</a>|";
+	$pattern = "|<a href=&#039;" . bp_get_root_domain() . "/" . $bp->members->slug . "/[A-Za-z0-9-_\.]+/&#039; rel=&#039;nofollow&#039;>(@[A-Za-z0-9-_\.@]+)</a>|";
 
 	$content = preg_replace( $pattern, "$1", $content );
 
Index: bp-groups/bp-groups-notifications.php
===================================================================
--- bp-groups/bp-groups-notifications.php	(revision 4042)
+++ bp-groups/bp-groups-notifications.php	(working copy)
@@ -253,7 +253,7 @@
 	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 */