Error message

• Warning: Cannot modify header information - headers already sent by (output started at /home/pornosn/public_html/ii-smile.com/includes/common.inc:2861) in drupal_send_headers() (line 1554 of /home/pornosn/public_html/ii-smile.com/includes/bootstrap.inc).
• Error: Call to undefined function mail() in DefaultMailSystem->mail() (line 79 of /home/pornosn/public_html/ii-smile.com/modules/system/system.mail.inc).