Here are the steps to have Domino and Hexamail coexist:
Move Domino to another port
To change the SMTP incoming port number:
1) Go to "Domino Administrator", "Server/Current Server Document"
2) Click on the "Ports" tab, then the "Internet Ports" tab,
3) Change the port number "25" to "2500" in the "TCP/IP Port Number" row of the "Mail (SMTP Inbound)"
4) Save the document, then stop and restart your Domino server.
5) To have Hexamail also process outgoing email messages: Open Lotus Domino Administrator and select the server from which you wish to forward mail. Click on the Configuration tab. Go to Server > Configurations. Click Edit Configuration. Select the Router/SMTP tab and then the Basics tab. Enter the IP address of the machine running Hexamail. Be sure to set up Hexamail smarthost settings to relay outgoing email to your ISP's smarthost.
Install and Configure Hexamail
1) Install Hexamail
2) You will now need to set the SMTP Server setting in Hexamail. If you are installing Hexamail on Windows, the setup program will ask you for the TCP/IP and port of your mail server during the configuration Wizard, or you can change this by opening the administration interface and setting the port on the SMTP Server settings page.
3) Next, set Hexamail SMTP Relay settings to point to your newly configured port.