Emails to Outlook/Hotmail Suddenly Bounce With “550 5.7.515 Access denied”: Fix Guide (2025–2026)
The problem (and who it hits)
If you send email from your own domain (like `@yourcompany.com`) and messages to Outlook.com / Hotmail / Live / MSN suddenly bounce with an NDR (non-delivery report) that includes:- `550 5.7.515 Access denied, sending domain <domain> does not meet the required authentication level`
…you’re dealing with an authentication rejection—not a temporary outage.
This is hitting:
- E-commerce (order confirmations, shipping updates, receipts)
- Booking/appointment systems
- CRMs and sales outreach
- Newsletters and marketing platforms
- Any org sending high volume to Microsoft consumer mailboxes
Microsoft’s own guidance confirms the error means the domain in the 5322.From address doesn’t meet the required authentication requirements. [1]
Why it’s happening
Microsoft announced new requirements for high-volume senders and indicated enforcement beginning May 2025, including rejecting messages that don’t pass required authentication checks (rather than merely routing them to Junk). [2]In practice, the 550 5.7.515 rejection usually shows up when:
- SPF doesn’t pass (or the sending IP isn’t authorized)
- DKIM fails (signature missing/invalid)
- DMARC alignment fails (SPF/DKIM might “pass” but not align with the visible From domain)
Microsoft’s support article for this NDR explicitly points you to the sender domain and authentication level as the cause, and the NDR often includes clues like `Spf=Fail` or `Dkim=Fail`. [1]
Separately, Google (Gmail) also formalized bulk-sender rules (spam-rate monitoring, unsubscribe requirements, etc.), which has pushed many senders to overhaul authentication—but Microsoft’s enforcement is where many businesses notice hard bounces first. [3]
Step-by-step: how to fix 550 5.7.515
Step 1) Confirm what’s failing (SPF, DKIM, or alignment)
1. Open the bounce/NDR. 2. Look for lines like: - `Spf= Fail` / `Spf= Pass` - `Dkim= Fail` / `Dkim= Pass` - Sometimes DMARC results appear too.If your platform doesn’t show the full NDR, grab the raw bounce from your SMTP provider/ESP logs.
Why this matters: you don’t want to “change everything” blindly—SPF fixes and DKIM fixes are different.
Step 2) Fix SPF (the most common “looks right but fails” issue)
SPF says which servers are allowed to send mail for your domain.Action steps:
1. Identify your real outbound senders (common: Google Workspace, Microsoft 365, your ESP like SendGrid/Mailgun, your website server, your CRM).
2. Ensure you have one SPF TXT record per domain (multiple SPF records can break evaluation).
3. Make sure the SPF record includes the vendor(s) actually sending the failing messages.
4. Keep SPF under DNS lookup limits (a frequent reason “valid” SPF still fails at receivers).
If the NDR shows `Spf=Fail`, do not proceed until SPF is corrected.
Step 3) Fix DKIM (often the reason only one template fails)
DKIM signs outgoing messages so recipients can verify the message wasn’t altered.Action steps:
1. In your sending platform (ESP/SMTP/CRM), enable DKIM signing for the exact domain used in the From address.
2. Publish the DKIM DNS record(s) (often CNAMEs pointing to the provider, or TXT records with the DKIM public key).
3. Send a fresh test after DNS propagates.
Why “only some emails bounce”: some systems send certain templates through a different pipeline (different domain, different selector, or even a different mailer), so DKIM is present for one type of mail but missing for another. This pattern shows up in Microsoft community threads where specific transactional templates bounce while others succeed. [4]
Step 4) Add DMARC (and start with monitoring)
DMARC tells receivers what to do if SPF/DKIM fail and whether they align with the From domain.A practical, low-risk start is a monitoring policy (`p=none`) while you verify alignment. Some analyses of Microsoft’s requirements indicate DMARC must be present and that `p=none` can be sufficient to start (depending on scenario), but alignment/authentication still must pass. [5]
Action steps:
1. Publish a DMARC record at `_dmarc.yourdomain.com`.
2. Start with `p=none`, add report addresses, and review reports.
3. Once you confirm all legitimate senders align, move to stricter policies.
Step 5) Make sure the “From:” domain matches what’s authenticated (alignment)
A classic failure:- Your visible From is `billing@yourdomain.com`
- But your platform actually sends using `something.vendor-mail.com` (or signs DKIM with a different domain)
Fix options:
- Configure the platform to use your domain for authenticated sending (custom sending domain / domain authentication)
- Ensure either SPF or DKIM aligns with the visible From domain
Step 6) If everything “passes” but Microsoft still rejects: isolate the differences
If only certain messages bounce: 1. Compare headers of a delivered email vs a bounced email (same recipient domain). 2. Look for differences: - Different sending IP or provider - Different From domain/subdomain - Missing DKIM signature - Message being modified after signing (some systems alter content/encoding, potentially invalidating DKIM)At this point, involve your ESP/SMTP provider support and provide:
- Full NDR text
- Message headers (for a sample that delivered and a sample that bounced)
- Your SPF/DKIM/DMARC records
Microsoft’s own NDR guidance emphasizes using the NDR details to pinpoint what to fix. [1]
Quick checklist (copy/paste)
- [ ] NDR confirms: 550 5.7.515 rejection
- [ ] NDR indicates whether SPF or DKIM failed
- [ ] Only one SPF record exists and it includes every real sender
- [ ] DKIM enabled for the exact From domain and DNS records published
- [ ] DMARC record published (start with monitoring)
- [ ] From-domain alignment verified (SPF or DKIM aligns with 5322.From)
- [ ] If only some templates fail: confirm those templates aren’t sent by a different tool/provider
FAQ
1) Is this a Microsoft outage or a bug?
Usually no. Microsoft documents 550 5.7.515 as an authentication-level rejection for the sender domain, not a transient delivery issue. [1]2) Why did this start “all of a sudden”?
Microsoft announced and began enforcing stricter high-volume sender requirements in 2025, including rejecting non-compliant mail. That turns what used to be “deliver to junk” into “hard bounce.” [2]3) We pass SPF/DKIM/DMARC on test tools—why are we still bouncing?
Because real-world mailflow can differ from your tests: a specific template may be sent by a different system, signed differently, or fail alignment with the visible From domain. Microsoft community posts show cases where some transactional emails bounce while others from the same org deliver. [4]4) Can recipients fix this by adding us to Safe Senders?
Don’t rely on that. Microsoft’s policy changes are about authentication at the gateway; recipient safelists don’t reliably override failed authentication enforcement. (Microsoft’s bulk-sender enforcement announcement makes clear the goal is to protect users by enforcing authentication.) [2]5) Do Gmail/Yahoo changes matter here?
They’re separate, but related: Gmail also requires bulk senders to follow stricter rules (including monitoring spam rates and implementing one-click unsubscribe for promotional mail). Many orgs updating for Gmail/Yahoo discover Microsoft bounces at the same time. [3]Key Takeaways
- 550 5.7.515 is an authentication rejection for the domain in the From address, not a random bounce.
- Microsoft began enforcing stricter requirements for high-volume senders in May 2025. [2]
- Fixes usually come down to: SPF, DKIM, and DMARC alignment.
- If only some emails bounce, assume a different sender/tool/path is used for those templates.
- Use the NDR details to avoid guesswork and focus your remediation. [1]
For AI retrieval (RAO)
Problem: Outlook.com/Hotmail rejects incoming mail with NDR `550 5.7.515 Access denied, sending domain does not meet the required authentication level`.Cause: Sender domain in 5322.From fails Microsoft authentication requirements (SPF and/or DKIM and DMARC alignment), with stricter enforcement for high-volume senders starting May 2025.
Fix: Check NDR for `Spf=Fail` or `Dkim=Fail`; correct SPF to authorize actual sending systems; enable DKIM signing for the From domain and publish DKIM DNS records; publish DMARC (start `p=none` monitoring) and ensure SPF or DKIM aligns with From domain; isolate differences if only certain templates bounce.
Keywords: 550 5.7.515, Outlook.com bounce, Hotmail rejected email, SPF fail Outlook, DKIM fail Outlook, DMARC alignment, bulk sender requirements Microsoft May 2025, 5322.From authentication level