Why Microsoft Is Junking (or Rejecting) Your Sends

Since May, Outlook/Hotmail rejects or junk-folders bulk mail that fails authentication alignment or lacks one-click unsubscribe. If you’re seeing 550 5.7.515 or dips on Microsoft cohorts, this is the checklist to run—today.

Today’s orders: Pass & align SPF/DKIM/DMARC, emit RFC 8058 one-click headers, then re-warm Microsoft with a lighter cadence and cleaner top-of-email CTA.

MXToolbox SuperTool Microsoft SNDS Gmail Postmaster Tools Yahoo Sender Hub

Symptoms We’re Seeing

Microsoft cohort CTR below Gmail Spike in junk placement post–May 5 SMTP rejections: 550 5.7.515 DMARC “none” with no RUA reporting No one-click (RFC 8058) header

Primary Diagnosis

Auth Misalignment + Missing One-Click

Outlook now rejects or spam-folders high-volume mail that doesn’t meet authentication requirements and one-click unsubscribe. Many beehiiv senders fixed Google/Yahoo in 2024—then stopped at DMARC p=none without reporting or alignment.

SPF: includes your ESP and aligns to your visible From: domain. (RFC 7208)
DKIM: signed by the same organizational domain you mail from. (RFC 6376)
DMARC: publish with rua= reporting first (p=none), then plan for quarantine/reject. (RFC 7489)
One-Click Unsubscribe: emit List-Unsubscribe + List-Unsubscribe-Post: List-Unsubscribe=One-Click. (RFC 8058, RFC 2369)

MXToolbox SuperTool Gmail Postmaster Microsoft SNDS Yahoo Sender Hub

Secondary Factors

Legacy reply-to domains, link-tracking clutter, and cold segments lift complaint rates—Microsoft punishes that faster than Gmail.

        Risk gauge: [■■■■■□□□] Microsoft-specific risk at ~60%
      

Treatment Plan (Deploy Over 7 Days)

1) Fix & Align Authentication

SPF: add/verify your ESP include and remove deprecated senders.
DKIM: rotate/selectors; sign with your brand domain, not a random sub.
DMARC: publish with rua= reports; investigate failures; plan enforcement path.

2) One-Click Unsubscribe

Ensure your sends include List-Unsubscribe and List-Unsubscribe-Post (RFC 8058). Verify in Gmail “View original.”

3) Microsoft Re-Warm

Create a Microsoft-only segment. Send 2–3 lighter emails with one top CTA, fewer links, and a clear benefit promise.

4) beehiiv Plays

Use Subscriber Center to step-down frequency for Microsoft readers and surface topic preferences. Add a 3-step save flow before unsubscribe.

5) Subdomain Strategy (Optional)

If you mail multiple products, split by authenticated subdomains (news.helpmynewsletter.com, promos.…), each with aligned SPF/DKIM/DMARC.

Vitals (Next 30 Days)

        Microsoft spam ≤ 0.2% • 0 hard “515” rejections per send • 100% one-click coverage • +10–20% Microsoft CTR
      

Observed Outcome

“We aligned DKIM to our root domain, added DMARC with RUA reports, and enabled one-click. Microsoft spam fell under 0.1% in two sends.”
— Ops Lead, 120K-sub publisher

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Microsoft is rejecting your newsletters (550 5.7.515 fix inside)

Why Microsoft Is Junking (or Rejecting) Your Sends

Auth Misalignment + Missing One-Click

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