Let’s assume you’re a company using your own domain (for example, mydomain.com), and your mailbox and outbound email is handled by a provider other than Google Workspace. Google is not part of your email infrastructure or authorized sending sources in any way.
Now, imagine you receive a Google Calendar invitation from another organization (e.g, example.com). You want to respond to this invitation—such as accepting, declining, or proposing a new time.
In some cases, when you reply to a Google Calendar invitation, the response bypasses your primary email infrastructure and is instead sent via Google’s servers. Since Google is not authorized to send email on behalf of your domain, this response fails authentication checks (SPF/DKIM alignment), which in turn causes the message to fail DMARC evaluation.
If the sender’s domain enforces a strict DMARC policy (such as p=reject), the calendar reply is rejected, preventing the event organizer from receiving your response, even though the email itself is legitimate.
This behavior can be confusing and disruptive, especially when valid calendar interactions are blocked.
Below are recommended approaches to mitigate this issue.
Recommendation 1: Use Out-of-Band Response Buttons (Recommended)
If your mailbox is hosted by a provider other than Google, you typically have two ways to respond to a Google Calendar invitation:
- Out-of-band response buttons
These are added by your mailbox provider and usually appear at the top of the email 
- In-message Google Calendar buttons
These are embedded directly in the email body by Google.
When you use out-of-band response buttons, the response is sent through your own mailbox provider’s servers, which are already authorized for your domain. As a result:
- SPF and DKIM align correctly
- DMARC passes
- The response is delivered successfully
However, when you respond using the Google-provided buttons inside the email body, the reply may be sent via Google’s infrastructure. Since Google is not authorized to send mail on behalf of your domain, the message fails DMARC checks and is rejected in accordance with the organizer’s DMARC policy.
Best practice: Always use your mailbox provider’s out-of-band response buttons when replying to calendar invitations.
Recommendation 2: Authorize Google in Your Domain’s SPF Record
If out-of-band responses are not available or do not resolve the issue, you can authorize Google as a valid sending source for your domain by updating your SPF record.
Add the following include mechanism to your domain’s SPF record:
include:_spf.google.com
This allows Google to pass SPF authentication when sending calendar responses on behalf of your domain, preventing DMARC rejection even when the reply is sent via Google’s servers.
Important Note for EasySPF Users:
If you’re using the EasySPF feature in EasyDMARC, make sure to add this include mechanism directly within the EasySPF dashboard:
- Click Add Source
- Select or add Google Workspace
- Save and apply the changes
Final Notes
By following one (or both) of the recommendations above, you can prevent Google Calendar invitation responses from failing DMARC authentication and being rejected.
If the issue persists or you need help reviewing your SPF, DKIM, or DMARC configuration, feel free to contact EasyDMARC Technical Support for further assistance.