On the other hand, this request sounds a little fishy from a technical perspective. Port 110 is used by the POP3 protocol for unencrypted access to electronic mail. The port is intended for end-users to connect to a mail server to retrieve messages. I can't imagine any reason that this port would be used in this case.
Port 25 is used by the SMTP protocol to send mail. The use of this port sounds a little more reasonable, but only if the request is that the copier be allowed to connect to your mail server on port 25. Port 25 would be used to send mail from the copier to the company, and there should be no reason you would have to allow inbound access to the copier on it.
The "how" part of your question depends upon your network topology. If the copier and your mail server are on the same network segment, you shouldn't need to change anything. If they're on different network segments, and those segments are separated by a firewall, you'll need to create a firewall rule that allows port 25 connections from the copiers to the mail server. See your firewall documentation for more on exactly how to do this.
This was first published in January 2009