contact_mail_page_submit in modules/contact/contact.pages.inc
Process the site-wide contact page form submission.
contact_mail_user_submit in modules/contact/contact.pages.inc
Process the personal contact page form submission.
hook_watchdog in developer/hooks/core.php
Log an event message
_update_cron_notify in modules/update/update.fetch.inc
Perform any notifications that should be done once cron fetches new data.
_user_mail_notify in modules/user/user.module
Conditionally create and send a notification email when a certain operation happens on the given user account.