error di header wordpress

minta bantuannya agan2..
Kenapa kadang selalu muncul error seperti ini di header website saya?
saya sudah install sampe dua kali dari wordpress 4.1 sampai saya downgrade ke 3.9.3 masih saja muncul error seperti ini?

sendmail: Can’t send mail: You have exceeded max_mails_per_day limit (500). Please try again later. Set-Cookie: visits=0 Set-Cookie: PHPSESSID=1c7124d21de87795cc329f0142544f54; path=/ Expires: Thu, 19 Nov 1981 08:52:00 GMT Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0 Pragma: no-cache Set-Cookie: wordpress_429f03a63e47b3b8a3e6e526c1d0a762=%7C1425218130%7C8871297b8135cce80a22339184bbab27; expires=Mon, 02-Mar-2015 01:55:30 GMT; path=/wp-content/plugins; httponly Set-Cookie: wordpress_429f03a63e47b3b8a3e6e526c1d0a762=%7C1425218130%7C8871297b8135cce80a22339184bbab27; expires=Mon, 02-Mar-2015 01:55:30 GMT; path=/wp-admin; httponly Set-Cookie: wordpress_logged_in_429f03a63e47b3b8a3e6e526c1d0a762=%7C1425218130%7C9fbb3d1fb5e18b5cd8eb80b3b5136604; expires=Mon, 02-Mar-2015 01:55:30 GMT; path=/; httponly X-Pingback: http://namadomain.com/xmlrpc.php Content-Type: text/html; charset=UTF-8 Link: ; rel=shortlink