In patch 4.4.0 and 10.2.7 the SendAddonMessage APIs were improved to return a new enum result code that provides expanded information on why a message wasn't sent.
The enum includes a code for not being in a group, which is returned when sending a message to either "PARTY" or "RAID" while not being in one. There's a couple of chat types however that currently don't eagerly check transmission eligibility and return the Success status unnecessarily.
While not in a group, sending a message to "INSTANCE_CHAT" returns a Success status. The client should ideally have a good view on whether or not it's in an instance group as many group-related APIs accept an LE_PARTY_CATEGORY_INSTANCE enum, so it would make sense in this case for the API to return the pre-existing NotInGroup status for such transmissions.
While not in a guild, sending a message to either "GUILD" or "OFFICER" returns a Success status. More annoyingly, in this case the server also spits back a system message saying the player isn't in a guild. It'd be more sensible for a new "NotInGuild" status code to be returned and the message not sent off.
In patch 4.4.0 and 10.2.7 the SendAddonMessage APIs were improved to return a new enum result code that provides expanded information on why a message wasn't sent.
The enum includes a code for not being in a group, which is returned when sending a message to either "PARTY" or "RAID" while not being in one. There's a couple of chat types however that currently don't eagerly check transmission eligibility and return the Success status unnecessarily.
LE_PARTY_CATEGORY_INSTANCEenum, so it would make sense in this case for the API to return the pre-existing NotInGroup status for such transmissions.