In fact, both Port 110 and 995 port are open status for listening the request from client no matter what version of your Exchange server. To use only 995 port on the premise that the certificate has been installed Exchange and applied for POP3 service.
Please understand that the communication is mutual between the Exchange server and the client. That means if the configuration on the Exchange ask for the SSL, the client must connect Exchange by using 995 port. If no such configuration exists there, you can free to select 110 or 995 port to connect Exchange server on the client side.
Regarding how to configure on the Exchange server so that both 110 and 995 port are available, please view the below content:
For Exchange 2003, open ESM, expand Administrative Groups, expand the Servers, expand Protocols, expand POP3, right click Default POP Virtual Server, click Properties, in the Access tab, click Communication button, uncheck “Require secure Channel” option.
For Exchange 2007, open EMC, expand Server Configuration, locate Client Access, in the POP3 and IMAP4 tab, double click POP3, in the Authentication tab, ensure “Plain text authentication logon” and “Secure logon” option are unchecked.