hokoto

That's the point: Google doesn't see the bounce back, so you won't be negatively affected.

I think the party host who is sending his invitations without using bcc is to blame here.

I use gmail mainly for business related mails and the default reply-all makes a lot sense - almost all the time other recipients ( managers, clients etc) are there to be kept in loop. If you forgot and just reply to it, then you have send the same mail again - or worse you never notice it.