We found some mails to recipients who uses specified IP of messagelabs.com as SMTP servers will failed with error return "
550 5.7.23 The message was rejected because of Sender Policy Framework violation -> 553 DMARC domain authentication fail..." . but next time send to same recipient can be succeeded. Seems some messagelabs.com IP can pass SPF/ DMARC verification but some can not. Could you please advise who messagelabs support can help? thanks.
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More Info for Email Admins
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Status code: 550 5.7.23
This error occurs when Sender Policy Framework (SPF) validation for the sender's domain fails. If you're the sender's email admin, make sure the SPF records for your domain at your domain registrar are set up correctly. Office 365 supports only one SPF record (a TXT record that defines SPF) for your domain. Include the following domain name: spf.protection.outlook.com. If you have a hybrid configuration (some mailboxes in the cloud, and some mailboxes on premises) or if you're an Exchange Online Protection standalone customer, add the outbound IP address of your on-premises servers to the TXT record.
For more information and instructions about configuring SPF records see Customize an SPF record to validate outbound mail sent from your domain and also External Domain Name System records for Office 365.
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