I forgot to post a follow up on this thread. I'd like to thank @girish for solving my problem. He responded quickly and arranged to ssh into my server to diagnose. He's been very patient and professional and I really appreciate it.
Basically the problem is due to MySQL addons not properly starting/building, so all apps using MySQL error out and cannot start or install. Hope the problem has been resolved in the final 2.4 releases 🙂
After disabling apparmor, I saw that mysqld would just quit without showing any error message or log output 😞 As a final thing, I just ended up moving platformdata/mysql to mysql-old and recreated containers again. That made mysql come up and then we restored all the apps.
Still a bit crazy/worrying that we hit this bug atleast twice now and there is no clear resolution.
Installed the app. It looks lie mailtrain creates an admin email that is <install name.app.domain> That email address is also used by campaign defaults. I tried sending a test email to it however and it did not go anywhere. In testing sending some emails, it does not appear can just change this email to anything you want. It must match the app domain???
Below you will see that the Blacklist:4 and Failed:2
The results are entirely based on the IP of your server and which VPS provider you got your server from. In fact, many providers like Amazon EC2, Google Compute don't let you send emails at all. I would recommend setting up a relay via Mailgun, Postmark or similar. It is the best way to ensure delivery of mail.
mail-tester runs your email via SpamAssassin. So make sure you send email to it with some real text! If you send fake text or empty emails, it will correctly mark your email as spam. I will put this note in our docs as well.
Upon some investigating, did find a polls utility like doodle in nextcloud. It allows you to share it with users but also share a public link. Pols can be text based or created using a calendar. Persons responding can answer a yes,no and maybe on whatever options are offered. https://github.com/nextcloud/polls