In this guide · 8 sections
- 01Why Outlook sends your email to Junk
- 02Outlook's sender requirements, in plain English
- 03Read the Microsoft error code first
- 04Fix it on the sending side: SNDS, JMRP and delisting
- 05Fix it on the recipient side: junk, quarantine and safe senders
- 06Content and habits that Outlook penalises
- 07Do it yourself or get help?
- 08Frequently asked questions
Short answer
Check that SPF, DKIM and DMARC pass for your domain, then look at the bounce or header: 5.7.515 means failed authentication, 5.7.606 to 649 means a blocked IP (delist at sender.office.com). If mail is only junked, ask the recipient to mark it Not junk or have their admin add an allow entry.
Why Outlook sends your email to Junk
Microsoft runs two separate filtering systems: one for consumer mailboxes (Outlook.com, Hotmail, Live, MSN) and one for business mailboxes on Microsoft 365. Both look at the same broad signals, but they are fixed in different places.
| Cause | Typical sign | Where to fix it |
|---|---|---|
| SPF, DKIM or DMARC failing | Error 5.7.515, or Junk at many Microsoft recipients | Your DNS records |
| Sending IP has a poor reputation | Error 5.7.606 to 649, or Junk across Outlook.com | sender.office.com, SNDS, your email provider |
| Your own account sent spam (Microsoft 365 sender) | Mail goes out via the high-risk pool and is widely junked | Secure the account; Microsoft 365 admin centre |
| Recipient's own filter or settings | Junk at one company only | Recipient's Outlook or their admin |
| Content and list quality | Newsletters junked, one-to-one mail fine | Your mailing practices |
Start by finding out which row you are in. Send a test to a personal Outlook.com address and to a contact at a Microsoft 365 company, and keep any bounce message you get back.
Outlook's sender requirements, in plain English
On 2 April 2025 Microsoft announced new requirements for high-volume senders to Outlook.com, enforced from 5 May 2025. They apply to domains sending more than 5,000 emails a day to Outlook.com addresses.
- SPF must pass for the sending domain.
- DKIM must pass.
- DMARC must exist with at least p=none, and align with SPF or DKIM (preferably both).
- Recommended: a From or Reply-To address that can receive replies, a working unsubscribe link, removing bounced addresses, and only emailing people who agreed to it.
Microsoft first said non-compliant mail would go to Junk, then updated the post to say it will be rejected with "550; 5.7.515 Access denied, sending domain does not meet the required authentication level". Most small businesses send far fewer than 5,000 emails a day, but Microsoft's FAQ says all senders benefit, and the same checks feed its normal spam filtering. Our SPF, DKIM and DMARC guide shows how to set the records.
Read the Microsoft error code first
If Outlook bounces your email instead of junking it, the code tells you what to do. Our bounce-back errors guide covers the general ones; these are the Microsoft-specific ones.
| Error | Meaning | What to do |
|---|---|---|
| 550 5.7.515 | Sending domain failed Outlook's authentication requirements | Fix SPF, DKIM and DMARC for the domain in the From address |
| 550 5.7.606 to 5.7.649 | Your sending IP is on Microsoft 365's blocked senders list | Request delisting at sender.office.com |
| 550 5.7.511 | Banned sender; the delist portal cannot fix it | Forward the bounce to delist@microsoft.com, as the error says |
| Bounce from Outlook.com consumer servers | Outlook.com filtering blocked your IP or domain | Use Outlook.com sender support |
Microsoft's delist portal guide explains the process: enter the email address that got the bounce and the IP address from the error, one of each per request.
Fix it on the sending side: SNDS, JMRP and delisting
If you send through Microsoft 365, Google Workspace or a newsletter service, the sending IPs belong to them, and they handle IP reputation. If you run your own mail server or a dedicated IP, you can monitor it yourself.
Confirm SPF, DKIM and DMARC pass
Open a message you sent to an Outlook.com address, view the message source and check the Authentication-Results line shows spf=pass, dkim=pass and dmarc=pass.
Sign up for SNDS
Microsoft's Smart Network Data Services shows how Outlook.com sees each IP you control, including complaint rates and spam-trap hits. You log in with a Microsoft account and prove you own the IPs.
Turn on JMRP
The Junk Mail Reporting Program, inside SNDS, sends you a report when an Outlook.com user marks your mail as junk. Remove those people from your lists.
Request delisting if blocked
For Microsoft 365 recipients, use sender.office.com. For Outlook.com consumer addresses, use the sender support form linked from the Outlook.com Postmaster site.
Separate bulk from business mail
Send newsletters from a dedicated service and subdomain, so complaints about marketing do not affect invoices and quotes.
Fix it on the recipient side: junk, quarantine and safe senders
If only one customer junks your mail, the fix is usually on their side. Send them this section.
- Outlook.com or Hotmail user: find your email in Junk and choose Not junk. Adding you to contacts helps future mail.
- Microsoft 365 user, mail in Junk: choose Not junk, or add the sender to Safe Senders in Outlook's junk email settings. That affects only their own mailbox.
- Microsoft 365 user, mail missing entirely: it may be in quarantine. Users can check at security.microsoft.com under Email & collaboration, Review, Quarantine, if their admin allows it.
- Their IT admin: Microsoft's safe sender guidance ranks the Tenant Allow/Block List as the best way to allow a trusted domain, ahead of mail flow rules and Safe Senders.
Ask the admin to allow your exact address or domain, not to switch off filtering. Allow entries skip some protection, so a narrow entry is safer for them. Note that Microsoft says Safe Senders lists are not honoured for its high-volume authentication rules: if you fail those, only fixing your DNS helps.
Content and habits that Outlook penalises
Authentication gets you through the door; behaviour decides the folder.
Outlook deliverability habits
Do it yourself or get help?
If your DNS records are right and only one recipient junks your mail, a polite request to their IT team is usually enough. If many Microsoft recipients are affected, or you see 5.7.515 or 5.7.606 errors, the problem is on your side and needs DNS and reputation work.
Our Emails Land in Spam fix (S$249, paid upfront, with 14 days of monitoring) checks SPF, DKIM and DMARC against Microsoft and Google rules, separates bulk mail and handles delisting requests. For DNS changes only, Domain & DNS Setup is S$99.
Frequently asked questions
Microsoft and Google use different filters and reputation data. Outlook may junk your mail because DMARC does not align, because the sending IP has complaints at Outlook.com, or because the recipient's Microsoft 365 admin has stricter policies. Check authentication results in a message sent to an Outlook.com address and look for any Microsoft error code.
It means Outlook rejected your message because the sending domain did not meet its authentication requirements. Microsoft introduced this for domains sending over 5,000 emails a day to Outlook.com. Make sure SPF and DKIM pass and a DMARC record exists with at least p=none, aligned with SPF or DKIM.
If the bounce shows an error between 5.7.606 and 5.7.649, go to sender.office.com, enter the email address that received the bounce and the IP address from the error, and follow the steps. For Outlook.com consumer addresses, use the sender support form linked from the Outlook.com Postmaster site.
Smart Network Data Services is a free Microsoft portal that shows how Outlook.com rates mail from IP addresses you control, including complaint rates and spam trap hits. It includes the Junk Mail Reporting Program, which tells you when users mark your mail as junk. It is useful only if you control your own sending IPs.
They can mark your email as Not junk and add you to Safe Senders in Outlook. If their company uses Microsoft 365, their IT admin can add your address or domain to the Tenant Allow/Block List, which Microsoft recommends over other allow methods. Ask for a narrow entry rather than turning off filtering.