Sometimes you’re part of spammy groups created against your consent and never want to join them. Problem is that if you just delete the invitation it seems that it’s not blocked forever; other people will send a message and you’re included in the recipients so you’re reinvited to the group.
Expected behavior
When I click on “delete” on an invite the group is deleted (works) and I don’t ever receive anything from that group
Actual behavior
I still receive messages from that group even though I never accepted an invitation
Leaving group works by sending a message to every member of the group that you leave the group, so everyone else removes you from the group member list. If it is a group created by the spammer, then sending a message or even a read receipt gives the spammer a signal that you have read the spam message, this is why we don’t do this as a default action.
One thing you can do to prevent the group from reappearing is muting and archiving it, then it is in your archive however if others keep sending messages there.