I have cron set to run a task for user pi (on my Raspberry Pi running Raspbian Stretch) every 15 minutes.
6,21,36,51 * * * * /usr/bin/mosquitto_sub -h Pi3Plus.local -v -C 1 -t weather >> weather.log
I also have ssmtp setup to send email via gmail.
Every so often the cron task fails to connect to the server, and generates an error message.
The problem is that it then attempts to send a message to user pi, which ssmtp changes to pi@gmail and sends to gmail, where it fails.
I have read the man for ssmtp, ssmtp.conf, cron, crontab but cannot find anything to stop these messages.
I could write a script to trap error messages in the cron task to prevent it generating an error.