Troubleshooting IceWarp communication on RedHat/CentOS

If you’re experiencing troubles with server communication, and have Icewarp installed on RedHat/CentOS server, it’s good practice to check following:

1. iptables – check what rules are applied via iptables -L
2. postfix – check the presence of this open-source Mail transfer Agent via postconf mail_version, which can block SMTP port 25; eventually uninstall it with the command yum remove postfix.
3. firewalld – check availability of the firewall via systemctl status firewalld, eventually uninstall it with command yum remove firewalld
4. nginx – check the presence of this server via command nginx, eventually uninstall it via command yum remove nginx
5. apache – check if Apache server is not blocking port 80 via this command: lsof -nPi | grep ":80 (LISTEN)"; eventually uninstall it via yum erase httpd httpd-tools apr apr-util and userdel -r "apache"
6. SELinux – check if SELinux is disabled by looking into its config: vi /etc/selinux/config; if it’s enabled, rewrite it to „disabled“