Cron job sends output for shell scripts but no for mysqldumps - Via Nullmailer

Question

I currently have two cron jobs in a server. One for a shell scrpit and another for a mysqldump.

Example:

43 16 * * * /var/backups_scripts/backups
46 16 * * * /usr/bin/mysqldump --login-path=bds-server --single-transaction database_name | /bin/gzip > /var/backups/bd_backup_$(/bin/date +\%d\%m\%Y_\%H\%M\%S).sql.gz

I have set up Nullmailer MTA. I can perfectly send an e-mail from terminal:

echo "Subject: sendmail test" | sendmail -v my_email

And I put that MAILTO line inside the cron tab (crontab -e).

Well, it's very strange that I receive outputs by email only when the shell script runs.

Regarding the mysqldump, no email is sent, and I was not able to see any reference to it on logs.

Any help would be very appreciated.

Tried other MTA, as msmtp, for example, without succes (the same happens).

P.S.: both tasks are being executed as I can see in their destinations.

P.S. 2: I really don't understood why the question was closed, sorry. My current job for mysqldump already have the scape charecter () right before the "%" symbol, as the suggested article mentions.