How much does access to the mail server on Centos disappear?

Question

iptables

Good morning!
The other day we transferred the mail server from the old cloud to the new one. A few days later, problems began, the server is working and access to it will be lost. When rebooting, it hangs at the stage iptables: unloandig modules. and if you force it to turn off and start, then it becomes like a number.