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Gmail starts applying new operational rules, non-compliant emails will be rejected.

Google has made Gmail’s ‘Guidelines for Email Senders’ fully operational.

The guidelines were published in October 2023 and have been in pilot operation since February 2024; from April 2024, emails that do not comply with the guidelines will be progressively rejected.

Google requires senders of emails to personal Gmail accounts to comply with the Guidelines for Email Senders in order to prevent fraudulent or unsolicited emails. These guidelines do not apply to Google Workspace senders.

The guidelines divide the conditions according to whether the number of emails sent per day is less than 5,000 or more than 5,000; the conditions that apply to senders who send less than 5,000 emails are as follows

Implementation of Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM) authentication in the domain.
Use of TLS (Transport Layer Security) connections for sending emails for which forward and reverse DNS records exist for the source domain and IP address
Maintain a spam transmission rate of less than 0.1%, but not more than 0.3%.
Use an email format compliant with RFC 5322 – Internet Message Format.
Do not spoof the ‘From:’ header
Add an ARC (Authenticated Received Chain) header to email forwarding by mailing lists and receiving gateways; the presence of the ARC header clearly indicates that the email is forwarded. For mailing lists, a ‘List-id:’ header is also required.

If the number of emails sent per day is 5,000 or more, the following conditions must also be met in addition to the above

Implement DMARC (Domain-based Message Authentication, Reporting, and Conformance) authentication in the domain.
For direct mail, the domain in the sender’s ‘From:’ header must match the SPF and DKIM domain
Marketing emails and unsubscribed emails must support one-click unsubscription. The unsubscribe link must also be clearly displayed in the body of the email

From now on, attempts to send emails that do not comply with the guidelines will receive a temporary error, and Google is urging email senders to audit this error to identify emails that do not comply with the guidelines and resolve the issue.

Google has also published a ‘Frequently Asked Questions about Email Sender Guidelines – Google Workspace Admin Help’, which should be viewed and resolved if there are any questions.