==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): latest
- Deployed with iRedMail Easy or the downloadable installer?
- Linux/BSD distribution name and version: Ubuntu 18 LTS server
- 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.
====

Okay, So now I am using iredmail in my office for a while it works perfectly fine most of the time. But I fail to understand what goes wrong non of the mail clients can connect to the server. All the ports (smtp, pop, pop3, imap, imaps) are just vanished. If I scan my ip with nmap it won't show these ports active. I have disabled the firewall and Ddos protection from my router but still this happens. The ports won't come back online even after i reboot the server and router.
Than suddenly after a while everything is back! I don't know after how much time but definitely after few hours it starts working back.

Any reason behind this?
some possible solution??

Note: running this on a raspberrypi 4 with ubuntu core and external hdd for the maildir. Everything works perfectly but somtimes don't understand what goes wrong.