eMClient 7 Server for at last 14 days error

The program we are using gives the following warning after a while?
firewall we have permission to access the following ip. Have my ip addresses changed?

eMClient allow ip adress

Yes, IP addresses change sometimes. Best is to use hostnames which your DNS will translate into IP addresses.

As a test, can you completely disable any anti-virus, firewall, proxy or VPN, then try again. Sometimes even restarting your router may resolve this.

I did all of these checks. No problem on computers with full internet access. those with limited access were connecting to the ip that I specified. It has stopped connecting lately. I think there is a change in the ip addresses. How can I learn new addresses?