Sending Mail from Cron in Ubuntu 20.04 LTS


I created a cronjob to back up my server content and wanted to test out emailing of errors when they occurred. To set this up, I installed msmtp and msmtp-mta to help send emails using an smtp server and bsd-mailx to test sending emails from terminal. The cronjob entry was:

*/1 * * * * echo "using default crontab mail functionality variable"

However, I got the following errors (check out /var/log/syslog):

Dec  2 06:14:02 ubuntu-docker-comic-misc-server cron[7901]: sendmail: the server did not accept the mail
Dec  2 06:14:02 ubuntu-docker-comic-misc-server cron[7901]: sendmail: server message: 551 5.7.1 Not authorised to send from this header address
Dec  2 06:14:02 ubuntu-docker-comic-misc-server cron[7901]: sendmail: could not send mail (account default from /home/rookie/.config/msmtp/config)
Dec  2 06:14:02 ubuntu-docker-comic-misc-server CRON[7899]: (rookie) MAIL (mailed 50 bytes of output but got status 0x0045 from MTA#012)

which confused me since msmtp should have had the from field set. Here's the config:

# Set default values for all following accounts.
tls            on
tls_trust_file /etc/ssl/certs/ca-certificates.crt
auth           on
logfile        ~/.msmtp.log

account fastmail
port 465
password some_password
tls_starttls off

# Set a default account
account default : fastmail

and msmtp logs showed that the appropriate from address was being used.

Dec 02 06:15:02 tls=on auth=on smtpstatus=551 smtpmsg='551 5.7.1 Not authorised to send from this header address' errormsg='the server did not accept the mail' exitcode=EX_UNAVAILABLE

I had made an incorrect assumption. I read msmtp docs and found that the set from = someemail configuration is used only when the original email is lacking the from field. A later release would support set_from_header on flag that would replace the from field with the config value. The version I was on is:

rookie@ubuntu-docker-comic-misc-server:~$ apt policy msmtp
  Installed: 1.8.6-1
  Candidate: 1.8.6-1
  Version table:
 *** 1.8.6-1 500
        500 focal/universe amd64 Packages
        100 /var/lib/dpkg/status

Next option was to find out if ubuntu's cron has support for setting a custom from address. Ubuntu uses a patched vixie-cron, but looking through the source code on vixie-cron's github page, the from field was either set up to the cron user or root.

There was a future patched version from ubuntu that provided support for a MAILFROM field, found in this bug discussion, but this was not available yet in my ubuntu release.

rookie@ubuntu-docker-comic-misc-server:~$ apt policy cron
  Installed: 3.0pl1-136ubuntu1
  Candidate: 3.0pl1-136ubuntu1
  Version table:
 *** 3.0pl1-136ubuntu1 500
        500 focal/main amd64 Packages
        100 /var/lib/dpkg/status

The fix I chose was to pipe the output to the mail command.

*/1 * * * * (echo "normal output" && cat asdfsfd) 2>&1 | mail -s "test" $MAILTO

This works because the mail command doesn't have a from field, so msmtp will set it from the config. I also pipe stderr to stdout so that it's also passed to the mail command. Only failing with this method is that if the cron job doesn't output anything, I'll still get a blank email. I don't have a problem with this though since the final cron job runs weekly.

I'll also be on the look out for when the updated versions of msmtp or vixie-cron are out and update my jobs.

Here's a great resource for things you should do when setting up cronjobs