Hello @Jon Mercer,
SPF is a standard method of email authentication. This protects your domain from spoofing and prevents outgoing messages from being marked as spam by receiving servers. It also defines the mail servers that are allowed to send email for your domain. In inbound mail servers, SPF checks incoming messages that appear to come from your domain to make sure they were really sent from servers you authorized.
Without SPF, inbound servers are more likely to mark messages sent from your organization or domain as spam.
As of November 2022, new senders sending email to private Gmail accounts must set up either SPF or DKIM. Google performs random checks on messages from new senders to private Gmail accounts to determine if they have been authenticated. Messages without at least one of these authentication methods are rejected or marked as spam with the 5.7.26 error. This requirement does not apply to existing senders. However, we recommend that you always set up SPF and DKIM to protect your organization's email and meet future authentication requirements.
For more information on SPF, click here.
For more information on DKIM, click here.
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