macOS catalina no longer sends email if job outputs to stdout
This issue was resolved with the macOS 10.15.4 update released in March 2020. 

After upgrade to 10.15.4, I started to receive emails from cron jobs I configured. Note, you have to set

MAILFROM and MAILTO environmental variables in cron in order to receive these emails.

Example:

MAILFROM=imac@home.domain.com
MAILTO=myuser@gmail.com

...

* * * * * sample_job