Here are the steps to have MDaemon and Hexamail coexist:
Move MDaemon to Another Port
1) Go to the "Setup" pull down menu, and choose the
"Primary Domain" choice. A window labeled "Primary Domain
Configuration" should appear.
2) Click on the tab labeled "Ports & DNS"
3) Locate the option that is labeled: "Listen for inbound SMTP events on this TCP port: ". Change the number "25" to another free port, such as "2500"
4) Click on the button labeled "Bind to new port values now"
5) Click on the "ok" button.
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.