Google Calendar Not Sending Email RSVP to My ICS File - icalendar

Question

I am attempting to send a meeting invite to both a user using outlook and a user using google calendar. In both cases, the ICS is recognized as a valid meeting request. In both cases I see the "accept/yes", "tentative/maybe", "decline/no" buttons as expected.
When the recipient clicks one of these buttons in Outlook, I receive the RSVP email back to me as expected and the event is added to the Outlook user's calendar (also as expected).
HOWEVER, when the google calendar recipient clicks on one of these buttons the event IS inserted into his/her calendar BUT no RSVP email is ever sent back to me.
NOTE: I am including a SENT-BY on the organizer but simplifying this does not change the problem.
The ICS file is as follows:
BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//My oncall calendar application//test.com
METHOD:REQUEST
BEGIN:VTIMEZONE
TZID:America/New_York
BEGIN:STANDARD
DTSTART;VALUE=DATE-TIME:20181104T020000
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
END:STANDARD
BEGIN:DAYLIGHT
DTSTART;VALUE=DATE-TIME:20180311T020000
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
END:DAYLIGHT
END:VTIMEZONE
BEGIN:VEVENT
SUMMARY:Meeting Time!
DTSTART;TZID=America/New_York;VALUE=DATE-TIME:20181022T142300
DTEND;TZID=America/New_York;VALUE=DATE-TIME:20181022T152300
DTSTAMP;VALUE=DATE-TIME:20181022T182300Z
UID:0.8860563089422712
SEQUENCE:0
ATTENDEE;PARTSTAT=NEEDS-ACTION;RSVP=TRUE;ROLE=REQ-PARTICIPANT:outlook_user#corpville.com
ATTENDEE;PARTSTAT=NEEDS-ACTION;RSVP=TRUE;ROLE=REQ-PARTICIPANT:gmail_user#gmail.com
CLASS:PUBLIC
CREATED;VALUE=DATE-TIME:20181003T115542Z
DESCRIPTION:Go online to update.
LOCATION:my desk
ORGANIZER;SENT-BY="mailto:no-reply#somewhereelse.io":MAILTO:me#example.com
PRIORITY:5
STATUS:CONFIRMED
BEGIN:VALARM
ACTION:DISPLAY
DESCRIPTION:Reminder
TRIGGER;RELATED=START:-PT1H
END:VALARM
END:VEVENT
END:VCALENDAR
The email msg is here:
Content-Type: multipart/alternative; boundary="===============8900875677198681530=="
MIME-Version: 1.0
Subject: Meeting Time!
From: My Mailer <no-reply#somewhereelse.io>
reply-to: me#example.com
To: outlook_user#corpville.com,gmail_user#gmail.com
--===============8900875677198681530==
Content-Type: text/plain; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Go online to update.
--===============8900875677198681530==
Content-Type: text/calendar; method="REQUEST"; name="invite.ics"; charset="UTF-8"
MIME-Version: 1.0
Content-Transfer-Encoding: base64
Content-Description: invite.ics
Filename: invite.ics
Path: invite.ics
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DQpFTkQ6VkNBTEVOREFSDQo=
--===============8900875677198681530==--

Answer 1

We also had the problem that Google Calendar does not send event invitation responses (RSVPs) to the inviting person from Microsoft Outlook/Exchange.
In our case, we discovered that all of the affected Outlook accounts have corresponding Google accounts associated with them, which are using the same email addresses as the Google accounts; i.e., registered on Google using the company's email address instead of a GMail address. GMail is not enabled for those accounts.
Google Calendar seems to be processing the responses from Google Calendar directly or internally, and does not send or forward the regular RSVP email response to the external / company email address.
We will check now
whether Google Calendar can be disabled for those Google accounts
whether Google Calendar has a setting to not mute/eat the RSVP responses or send CCs in all cases
whether enabling GMail for those Google accounts resolves the problem.

Answer 2

OK. I found my error. If you are using a GMail based email address for the organizer, it appears that Google Calendar will not send a RSVP reply unless it verifies that the email address did in fact create the google calendar. If you use an arbitrary email address (that you own, for example) then it sends it back no problem.

Answer 3

The can happen when the inviter's email address is associated with a Google Workspace Account and the invitee is using Gmail (regardless if it's personal or via Google Workspace). In this case, Google will prefer to internally process the RSVP (rather than send it out through the Internet) which then ends up in the wrong place.
In my case, because I (the inviter) no longer use Google Workspace for email and calendar, I simply turned off my Google Workspace account's Gmail and Calendar apps via admin.google.com > Apps > Google Workspace > Service Status.
After doing this, all RSVPs from all invitees (including invitees using Gmail), started making their way back to my non-Google-hosted calendar app.