Using calendar notifications for a custom domain. We have SPF, DKIM and DMARC correctly setup and they work great for email sent directly by users. 

However, notifications sent by calendar events always fail the DMARC check. Even though both SPF and DKIM pass, the DMARC check fails and I understand that it's because the envelope sender is different from the header sender. Envelope uses something like @sender.zohocalendar.com, while the header sender is the users own email.

This makes it impossible to switch the DMARC policy from "none" to anything higher and is a major issue that prevents us from moving the while organization mail to Zoho.

Any help or ideas are greatly appreciated.