Set up multiple AirMessage users on a single Mac computer
Special thanks to Dhruv Sachdeva for putting together this guide
On your Mac, navigate to System Preferences > Users & Groups. Click the lock to enable edit access, and then click the + icon above the lock to create a new user account.
Next, click your account name at the top-right of the screen next to the time and date. Click the new account name to “fast-switch” to it. Follow through the standard account setup procedure, and sign in with this user’s Apple ID. Set up AirMessage with this user’s Google account.
You should now be able to use AirMessage with both accounts running on this Mac. Please be sure to keep each Mac user account that uses AirMessage logged in.
Ensuring a reliable experience
It may be helpful to specify the AirMessage macOS server application to automatically run on start-up in the Users & Groups settings, just in case the Mac restarts. Likewise, you can then also enable the Mac to automatically power-on after a power failure in the Energy settings.
Also, installing remote access software on your Mac will allow you to easily connect to it when away from your network, just in case if ever needed. There are many great free options.
Setting up with manual server access
If you’re manually entering your server details in the AirMessage app rather than signing in with a Google account, there are a few extra steps that will need to be taken.
On the secondary account on your Mac, open up AirMessage’s preferences window, and change the port. The port number must be a number that isn’t already in use (your first installation of AirMessage is likely using the default port number,
You will also have to create another port forwarding rule for this new port number that points to the same Mac computer.
Finally, each AirMessage user requires its own server address with the associated port in the Android app. Apart from the port, the server addresses will be almost identical; basically, the DDNS or public IP address part is the same. For example: Bob uses
mynetwork.ddns.com:1359, and Marie uses