Home › Guides

Emails going to junk in Outlook or bouncing from Hotmail? How to fix it

Updated 10 November 2026 · by Mohamed, Growth with MK

Plenty of UK customers still use Hotmail, Outlook.com, Live and MSN addresses, and many businesses use Microsoft 365. If your emails land in their Junk folder, or bounce back with an error, this guide covers what Microsoft looks at and what to change.

What changed in 2025

From 5 May 2025, Microsoft began enforcing authentication for high-volume senders to its consumer services (Outlook.com, Hotmail, Live, MSN). Domains sending more than 5,000 emails a day must pass SPF and DKIM and publish a DMARC record (at least p=none) that aligns with the From address. Non-compliant mail is rejected with:

550 5.7.515 Access denied, sending domain [yourdomain] does not meet the required authentication level.

Most small businesses send far fewer than 5,000 a day, but the same checks feed into Microsoft's filtering for everyone, so unauthenticated mail is more likely to go to Junk.

Common causes

  1. No DMARC record, or SPF/DKIM failing. Of 747 UK small-business domains we checked in November 2026, 46% had no DMARC record.
  2. A sending tool that isn't aligned with your domain, such as a newsletter platform or website sending "as" you but signing with its own domain.
  3. Your IP or domain has a poor reputation with Microsoft, often after a burst of sending or spam complaints.
  4. The recipient's own rules: a Junk filter set to "High", or your address on their blocked senders list.

How to diagnose it

  1. Read the bounce. A 550 5.7.515 means authentication. 550 5.7.1 / "blocked" messages with an S3150-style code usually mean your sending IP is on Microsoft's blocklist, often a shared IP at your host or provider.
  2. Check the headers. Send a test to an Outlook.com address, open it in Outlook on the web → three dots → View → View message details. Look for spf=pass, dkim=pass and dmarc=pass in Authentication-Results.
  3. Run the free domain check for a quick view of SPF, DKIM, DMARC and MX.

How to fix it

  1. Publish one SPF record listing every service that sends as you.
  2. Turn on DKIM everywhere you send from. In Microsoft 365 it's in the Defender portal under Email authentication settings → DKIM. Each domain has two CNAME records to add.
  3. Add DMARC: v=DMARC1; p=none; rua=mailto:you@yourdomain, then tighten.
  4. If your IP is blocked, ask your provider. If you run your own mail server, use Microsoft's sender support form (linked from the bounce) to request delisting, and sign up to its Smart Network Data Services (SNDS) to see your IP's reputation.
  5. Ask regular contacts to add you to their Safe Senders. It helps immediately while the domain fixes take effect.

Gmail users affected too? See why business emails go to spam.

Frequently asked questions

I only send a few emails a day. Do Microsoft's rules apply to me?

The hard 5,000-a-day rejection rule applies to high-volume senders, but Microsoft's filters use the same SPF, DKIM and DMARC results for everyone. Fixing them helps any sender.

What does 550 5.7.515 mean?

Microsoft rejected the email because your domain didn't meet the authentication level it requires: SPF and DKIM passing and a DMARC record aligned with your From address.

My email reaches Gmail but not Hotmail. Why?

Providers filter independently. Microsoft weighs IP reputation heavily, so a shared server with a poor reputation can be blocked by Outlook.com while Gmail accepts the same email.

Will moving to Microsoft 365 fix it?

Not on its own. You still need SPF, DKIM and DMARC set up for your domain in Microsoft 365, and any other tools sending as you need authorising too.

Check your domain in 10 seconds

See your DMARC, SPF, DKIM and MX score out of 10, with fix steps for your email provider.

Run the free check

Related guides