Messages are automatically redirected to similar addresses
This is a known issue related to the way that the macOS Messages app handles sending messages to people with multiple contact addresses. Messages may automatically redirect outgoing messages to another address that isn’t registered with iMessage, if it happens to be listed under the same contact.
In order to get around this issue, you will have to remove all contacts saved on your computer that is running AirMessage Server. Please note that this will not delete any contacts from iCloud, from Google Contacts, or from any of your other devices.
Unlinking cloud contacts
First of all, disable contacts syncing for any online accounts on your Mac. Open System Preferences and navigate to Internet Accounts. For every account listed, please ensure that “Contacts” is unchecked in the detail list.
Removing local contacts
If you have any contacts saved locally on your Mac, you may wish to remove those as well. To do so, open the Contacts app, and delete all remaining contacts in the list.