CiviMail won't send mailings; start/completed date is "0th, 0 12:00 AM"
I'm not sure what causes this - but an upgrade on a site of mine (MySQL 5.5, Debian 8.9) caused my civicrm_mailing_job database table to not allow NULL values for start_date and end_date.  Since a NULL start date is a condition for sending emails, this causes CiviMail to fail.

To fix this, you need to run the following SQL commands:

ALTER TABLE civicrm_mailing_job MODIFY start_date timestamp null;
ALTER TABLE civicrm_mailing_job MODIFY end_date timestamp null;