We use the RSVP feature of the calendar and were using the Action feature "Email All Attending". Over the past few months this feature has been failing. It started with only one or two organizers having problems but recently seems to be affecting every organizer and has become so unreliable that I am telling people not to use it.
I haven't tried today, but in the past I was able to send messages that the attendees received, but the other Owner failed, so it is not just permissions. I can not see any pattern in the email host of the sender or the recipient.
Messages that are sent from New Topic, Calendar Invites, and Replies to Attendees all go through. Just email to attendees fails, which makes me suspect an error in how that message is sent.
I use gmail and see the following in my Recent Bounces -
gmail-smtp-in.l.google.com: 550 5.7.1 [18.104.22.168 12] Our system has detected that this message is likely unsolicited mail. To reduce the amount of spam sent to Gmail, this message has been blocked. Please visit https://support.google.com/mail/?p=UnsolicitedMessageError for more information. h13si714500ild.132 - gsmtp
Thanks for looking into this,