I'm not sure whether this is security or Core OS.
I'm running macOS 10.13.6. I didn't upgrade to 10.14 because I've been running Server.app, and need to keep some websites going.
On January 17, 2019 I installed a security update from Apple, and command line bash scripts are now unable to send email messages. If I use type the /usr/bin/mail command manually, it seems to work, and the process returns a status code ("echo $?") of 0. But those messages do not get delivered.
For a script that is scheduled to run daily, I actually get emailed failure notices from the "Mail Delivery System" saying the messages could not be delivered:
delivery temporarily suspended: connect to
127.0.0.1[127.0.0.1]:10024: Connection refused
Any information about what might be going on would be appreciated.