>>>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?
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>>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.
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>>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.
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>>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.
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>Update: The above applies if your machine is the server. If you access another SMTP server, then your machine is the client, and doesn't need a fixed IP address.

I re-read the customer message and I think I understand the issue better. Let me explain to you and Borislav to see if there is a solution:

The customer - for security reasons - restricts the use of SMTP. Therefore, they control access on the Exchange server via a list of authorized IP addresses. Therefore, they assign a bunch of static IP addresses for PCs using my application and enter those IPs in the list of authorized (on the Exchange server). Therefore, in their case, if a PC changes the NIC or PC itself gets replaced, the user has an issue emailing. And we have hit this problem a couple of times already. So they want to know if my application can send email from the server and not from the client PC. I suppose the SMTP will be the same but initiated on the server instead of on the client PC.

Now, does it make sense and is it possible to do what they want?