Send & Receive Issues

How to Fix Microsoft Bookings Emails Blocked by Gmail SPF Error 5.7.26

Emma Brown Oct 15, 2026 869 views

Question details

Microsoft Bookings emails sent to Gmail addresses are being rejected due to an SPF authentication failure.

How to Fix Microsoft Bookings Emails Blocked by Gmail SPF Error 5.7.26

Product: Microsoft 365 Bookings
Device & OS: not provided
Scenario: An organization uses Microsoft Bookings to schedule appointments, but the automated confirmation emails sent to clients with Gmail accounts are blocked and fail to deliver.
Observed behavior: Gmail rejects the incoming emails with Error 5.7.26, indicating that the sender domain's SPF record does not authorize the sending IP address.

Before you start

You will need access to your domain registrar's DNS management portal and administrative privileges in the Microsoft 365 admin center to update your email authentication records.

Solution 1Recommended

Update the Domain SPF Record for Microsoft 365

Modify your domain's DNS records to authorize Microsoft 365 and Bookings to send emails on behalf of your domain.

Sender Policy Framework (SPF) is an email authentication method designed to prevent domain spoofing. When Gmail receives an email from Microsoft Bookings, it checks your domain's SPF record. If Microsoft 365 is not listed as an authorized sender, Google blocks the message to protect users from potential spam.

Log in to your DNS provider

Navigate to the website of your domain host (e.g., GoDaddy, Cloudflare, Namecheap) and sign in. Locate the 'DNS Management' or 'Name Server' settings page for the domain associated with your Microsoft 365 account.

Locate the existing SPF record

Look through your DNS entries for a TXT record that begins with 'v=spf1'. If you already have one, you will need to edit this existing record rather than creating a new one.

Add the Microsoft 365 authorization

Edit the TXT record to include the Microsoft 365 Exchange Online service. Ensure 'include:spf.protection.outlook.com' is in the string. A standard, correctly formatted Microsoft 365 SPF record looks exactly like this: 'v=spf1 include:spf.protection.outlook.com -all'.

Save and allow time for propagation

Click 'Save' or 'Update' to apply the changes to your DNS zone. Keep in mind that DNS changes can take anywhere from 15 minutes to 48 hours to fully propagate across global internet servers.

Important: Do Not Create Multiple SPF Records: A domain must only have one SPF TXT record. If you use multiple services (like Mailchimp and Microsoft 365), you must combine their include statements into a single line, for example: 'v=spf1 include:spf.protection.outlook.com include:servers.mcsv.net -all'.

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Frequently Asked Questions

Why are only my Gmail clients failing to receive Bookings emails?

Google enforces extremely strict email authentication policies to combat spam and phishing. If your domain's SPF, DKIM, or DMARC records are missing or misconfigured, Gmail will outright block the incoming messages, whereas less strict email providers might still deliver them to a spam or junk folder.

Can I bypass Error 5.7.26 by resending the blocked email?

No. Error 5.7.26 is a permanent server-level rejection caused by failed authentication. Resending the message, modifying the subject line, or trying a different recipient at the same provider will result in the same error until the underlying DNS SPF record is corrected.

How long will it take for Bookings emails to work after I fix the SPF record?

While you save the DNS changes instantly, global DNS propagation typically takes between 15 minutes and 24 hours. Once Google's servers query the newly updated SPF record, your Microsoft Bookings emails will successfully deliver to Gmail recipients.

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