Messages sending to deleted contacts?

This is almost always due to a failure to sync after making ANY change - not just changes to the contact list. 

More than you wanted to know: In a message, each recipient who is a contact is identified by a small number (rather than by the SMS number or email address). On the server, the number is converted to the appropriate "real" address. The server then sends the message on to the real address. In order for this to work, the server and the device must agree on the number for each contact. These things are supposed to be "aligned" by a sync.

I have seen posts suggesting that a sync does not always fix it. Those posts suggest resetting the device to factory defaults - followed by a sync. I am not sure why this would help, but some people report that it does. Full reset is a big hammer. You lose all user data on the device. And you must repeat the outdoor portion of the activation sequence.

Since this is an old contact, open a support ticket if the problem continues after a sync. I AM a little concerned by the use of Earthmate. This introduces another variable, especially if you allowed Earthmate to access your contacts on the phone.

Thanks for your help! I experienced this behaviour on my prior inReach device, and it transferred over to my new, out-of-the-box Mini when I first set it up. I do sync regularly (probably hundreds of times now), but not after making every single change to my account. E.g. if I change details of a message, I'll save the change online, make a few other changes to messages, and then sync all the changes to my device in one go. Syncing after every single "save" would be tedious and slow. 

The problem persists even without Earthmate. In fact, I rarely (never) use Earthmate, but was just fooling around with it to send messages and noticed the issue remained. Just tested again now (without Earthmate), and a preset message I sent from my device to my personal email and phone number again gets copied to my iPhone Messages chat with an unrelated person. I've synced many times in the last few days, including after removing this unintended contact from everything I can find in my Garmin account and devices. 

Sure looks like some corrupted data on the backend, so I'll open a ticket. I don't mind trying a factory reset, but like I said, this problem persisted with a new device out of the box. 

Did not mean to imply that you should sync after every single change, one at a time. Rather that you should sync even if what you changed was not directly contact related.