what is group message ?

Thanks for the clarification.  

Another question: so group messaging via the app is working for ir addresses, emails and cell phone numbers?

I deleted the original message I had posted as I was incorrect. I did some testing on this and verified that what the manual says is correct. The app will do group messages with SMS only. If you start a group message with an inReach address or e-mail it will create individual messages and replies then. 

Even when sending to more than one SMS address (from the app), you have choice between "Message" (which is a group message) or "Post" (which sends the same message to all recipients but keeps replies separate - that is, replies come back only to the sender of the "post").

Could, perhaps, be a little clearer in the app itself. 

https://support.garmin.com/en-US/?faq=icTGocuFYw88BFNWburNv8&productID=893837&tab=topics&topicTag=region_messagescontacts

You must dig down into one of the "Sending a Message..." subtopics to find this nugget.

Ok, thanks again. That was not really clear to me. So, if the user thinks he is going to start a group message with an inReach address or e-mail, he will get charged as much user he has used. So that is an important thing to know.

Thanks, twolpert. Yes, there it is clearly defined: "Group messages cannot contain email, inReach, or social addresses." 

Should be placed visible in the manuals, too.  Garmin has created a lot of useful hints/explanations, the user just has to know where/how to find them. That should be clearer somehow.

If the user wants to create a group message via the app and is using 2 sms numbers, 1 ir and 2 email addresses, he is sending out 4 messages; if the user is using the messenger (because he thinks that is working with the messenger, too), he is sending out 5 messages...

I was unable to find a manual for the app. However, there is a whole support "section" on the app (as distinct from the device).

https://support.garmin.com/en-US/?productID=893837&tab=topics

@Garmin-Leslie: ok, great, we have cleared here a lot of stuff, today.  But one thing is really not clear to me: why can’t the user send a group message via messenger or ir widget??? Where is the limitation? Why?

volker The limitation is the inReach messaging via satellite. None of the inReach devices allow for group messaging through satellite communication. The messenger itself along with the IR widget strictly uses single satellite messages. The messenger app allows for group messaging solely in the app because it uses wifi and cellular data to transmit. With satellite messaing you can send messages out to multiple contacts but they will only come back as individual replies. 

Thanks