>Yes, of course, you are right. Let me describe the problem. And some of it I don't quite understand but I am sure you will. The customer tells me that they want to use DHCP to get IP address dynamically (on client PCs). But they say that they cannot do it because of my application. Supposedly, if I understand correctly, the SMTP is somehow "tied" to IP. And if IP of the machine changes, the SMTP cannot be used. Therefore for PCs that use my application they have to assign static IPs. Does it make sense?

Yes, it makes sense. Different kinds of servers should have fixed IP addresses. This includes print server, file servers, etc. Having the IP address change regularly - which may happen with DHCP ("assign IP address automatically") - is problematic in such cases.

If you have any kind of server (any kind of program that other computers will need to access), you should assign the computer a fixed IP address.

This should be no big deal for configuration; just configure that one machine for a specific IP address. Other machines (the workstations) can still get their IP address automatically, through DHCP.