550 5.7.515: Outlook.com Says Your Domain Doesn't Meet the Authentication Level

A 550 5.7.515 bounce means Microsoft refused your email to an Outlook.com, Hotmail or Live address because your domain’s email authentication didn’t pass its checks. It is Microsoft’s version of Gmail’s 5.7.26 error. The fix is in your domain’s DNS records.

The bounce usually comes from ‘Microsoft Outlook’ or ‘Mail Delivery System’ and contains:

550 5.7.515 Access denied, sending domain yourbusiness.co.uk does not
meet the required authentication level.

The exact wording varies a little. The code 5.7.515 is what matters.

At the time of writing (last checked 6 October 2026), Microsoft’s rule covers domains that send 5,000 or more emails to its consumer addresses (Outlook.com, Hotmail.com, Live.com and MSN.com), all from the same domain. Microsoft’s announcement puts that at 5,000 a day. Those domains must have:

• SPF and DKIM records, and both checks must pass.
• DMARC, at least at p=none, and it must pass: at least one of SPF or DKIM must match the domain in the From address.

Microsoft’s announcement said it would start refusing emails that don’t meet this, with a 5.7.515 bounce, from 5 May 2025.

Most small businesses send far fewer, yet some still report this bounce, often after a newsletter or a burst of invoices or reminders. Whatever the volume, it means your domain’s records are not complete, and the same gap is likely to be hurting your delivery to other providers too.

This bounce only affects Outlook.com and other Microsoft consumer addresses. Business mailboxes on Microsoft 365 use different rules.

1. No DMARC record. Many domains have SPF and DKIM but never added DMARC. Microsoft’s rule needs it, even at the gentlest setting.
2. DKIM not switched on for your own domain. Microsoft 365 and Google Workspace sign with their own domain until you switch on DKIM for yours, so your DKIM doesn’t match your From address.
3. A mailing service sending as your domain without its own records. Newsletter, invoicing and booking systems need adding to your SPF record and their own DKIM setting up. Bulk sends are what usually push a domain into Microsoft’s checks.
4. A broken SPF record: two SPF records on one domain, a typing error, or one that names an old provider.

1. List everything that sends email as your domain, especially anything that sends in bulk: newsletters, invoices, reminders, booking confirmations.
2. Check your SPF record. There must be exactly one TXT record starting v=spf1, including every service on your list. Each service’s help pages give the value to add.
3. Switch on DKIM for every service, using the records each one gives you. Copy them exactly.
4. Add a DMARC record if you have none. Create a TXT record named _dmarc with the value v=DMARC1; p=none; rua=mailto:you@yourbusiness.co.uk. This satisfies Microsoft’s rule without blocking anything, and the reports it sends show you what is sending as your domain.
5. Resend. Microsoft does not deliver a refused email later, so anything that bounced needs sending again once the records are fixed.

DNS changes usually take effect within an hour, and occasionally up to 48 hours.

Send a test email from the address that bounced to a Gmail address (Outlook.com doesn’t show these results as clearly). Open it, click the three dots, choose ‘Show original’, and check SPF, DKIM and DMARC all show PASS, with your own domain next to DKIM. Do the same for each system that sends as your domain. My guide to reading email headers explains the details.

With one email provider and one newsletter tool, the steps above are usually under half an hour. It is worth asking for help when several systems send as your domain, when you are not sure which one caused the bounce, or when your DMARC reports show senders you don’t recognise.

• 550 5.7.26: Gmail says the sender is unauthenticated, Gmail’s version of the same problem.
• Why emails bounce, for other bounce codes.
• Google, Yahoo and Microsoft email rules, for what each provider expects.

Need help fixing this?

I provide:

• Free initial assessment
• Clear explanation of the issue
• Fixed-price solutions
• UK-based support

Forward me the 5.7.515 bounce and I’ll check your domain’s records against Microsoft’s rules and fix what is missing.