Index: wp-includes/formatting.php
===================================================================
--- wp-includes/formatting.php	(revision 25083)
+++ wp-includes/formatting.php	(working copy)
@@ -1855,6 +1855,7 @@
 		return apply_filters( 'is_email', false, $email, 'domain_no_periods' );
 	}
 
+	$i = 0;
 	// Loop through each sub
 	foreach ( $subs as $sub ) {
 		// Test for leading and trailing hyphens and whitespace
@@ -1866,6 +1867,10 @@
 		if ( !preg_match('/^[a-z0-9-]+$/i', $sub ) ) {
 			return apply_filters( 'is_email', false, $email, 'sub_invalid_chars' );
 		}
+
+		// Test for fewer than 2 characters in last sub
+		if ( ++$i === count( $subs ) && strlen( $sub ) < 2 )
+			return apply_filters( 'is_email', false, $email, 'last_sub_too_few_chars' );
 	}
 
 	// Congratulations your email made it!