Better to open a support ticket regarding that, but most likely there's a problem with connecting to our Amazon SMTP servers, so before creating a ticket I suggest to make sure that AWS servers can be reached from your machine and no-replyatcloudberrylabdotcom is white-listed in your mail filter.

I'm testing the free version at the moment ~ so I can't open a ticket.
Did a little more digging and found some entries in the logs:

2020-02-13 17:51:31,809713 [ERROR]: [ CBB ] [ 16 ] Error can't init ssl
2020-02-13 17:51:31,810710 [ERROR]: [ CBB ] [ 16 ] Error: can't init ssl context!

They do not get any more informative if I increase the log level to debug :(

What are the servers and ports it is trying to connect to? If I try to look them up (dig cloudberrylab.com MX) I get Google mail servers.

The CBB instance right now is in an Amazon Lightsail container, it took a bit of work to get that thing to send mail at all , but it does send mail externally.

CBB was sending notifications initially
I had to change the plans to root.root ownership to get it to backup some files/folders
that's when it (mail notifications) stopped working
changing ownership back or trying to create a new plan still show the "cannot reach" error.