==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): 0.9.9 MARIADB edition.
- Deployed with iRedMail Easy or the downloadable installer? Donwloadable  versione
- Linux/BSD distribution name and version: Ubuntu LTS and/or Debian 9
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MariaDB
- Web server (Apache or Nginx): Nginx
- Manage mail accounts with iRedAdmin-Pro? NO
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====

I don't know if you are already aware of this problem:
ufw 0.35 does not start after booting.

It seems to be a known bug, but the bug behaves differently depending on the operating system in use:

1. ubuntu LTS: ufw does not start nor configures the firewall rules. It does not start as a service, not even adding a command in rc.local or adding a line '@reboot root ufw enable' to the cron file.

2. Debian 9: although after the boot, the ufw status command responds 'Status: inactive' but the rules are loaded instead, because the mail server is working properly, and by checking with nmap the ports are actually open.

So until a patch or update of ufw 0.35 is issued, keep it in mind before you go crazy trying to figure out what the problem is.

JC