How to fix calendar invites not sending from iCloud accounts

If you use an iCloud calendar and invite an iCloud user to a calendar event, they’ll get a notification in the calendar app. If you invite a non-iCloud user, they’ll get an email notification — except when they don’t, and it might be confusing to figure out why.

To understand why this is happening, it’s important to realize that invitations sent from an Apple ID to another Apple ID are, by default, kept in Apple’s ecosystem and routed to the recipient as a notification rather than an email. If your recipient has an Apple ID that’s a third-part email address, such as a Gmail address, and uses the Gmail calendar, your invite likely won’t make it to them because of this.

The solution is to ask the recipient of your invite to sign into iCloud and change a setting within their iCloud calendar settings to enable email delivery of notifications. After signing in, the recipient should open Calendar, click the gear icon in the bottom left corner, click Preferences, Advanced, and change the invitations setting to “email to…”

I’ve prepared a snippet below that you can use to pass this information on, in case someone doesn’t get a calendar invite. Feel free to use this freely and modify it as the need arises:

If you were invited to a calendar event that I sent you, you should have received a notification to inform you of it, which includes an option to respond. If you didn’t receive this notification, it’s very likely that you have an Apple ID set up with the same email address. The reason that you didn’t receive my notification has to do with the way that notifications are passed through Apple’s system, and it may have redirected the notification to your iOS or MacOS calendar instead of your email, or vice-versa, depending on how you have it set up.

To make sure you don’t miss these notifications again, I encourage you to change the setting within your iCloud account to best fit your notification preferences. To do this, just follow the short instructions below:

First, sign into your iCloud account and go to your calendar by following this link:

Next, click the gear icon in the lower left.

Then click Preferences, Advanced, and locate the invitations setting on this screen.

Set it to email if you want an email, or in-app notifications if you want that instead.

Last, click Save.

I’ve had to do this once myself, so I can speak to it solving the issue.

Source: iCloud calendar not sending invites (StackExchange)