Cron has stopped executing jobs, how to identify the problem?

Question

ubuntu

The cron log looks like it is not clear where to dig.

Answer 1

I think cron is working.
But the job itself, which is in the cron, fails, the cron tries to send a letter, but judging by the sendmail error, the letter is not sent anywhere.
It is better to dig towards fixing the mail or try to run the cron job manually.