Your emails reach Gmail inboxes without trouble, but anyone on Outlook, Hotmail or Live says they found you in junk. It’s one of the most common problems we see from businesses in the UK and Ireland, and Microsoft’s filtering works differently enough from Gmail’s that the usual fixes don’t always carry across.
Here’s the checklist we work through when a client’s mail is going to junk at Microsoft, in the order that usually finds the problem fastest.
Why Microsoft matters so much in the UK and Ireland
A big share of UK and Irish personal email addresses sit with Microsoft: hotmail.co.uk, live.co.uk, live.ie, outlook.com, msn.com and the rest. Plenty of people set up a Hotmail address years ago and never moved. If you sell to consumers, the Microsoft domains are often one of the biggest groups on your list after Gmail.
It matters for B2B too. Lots of UK and Irish businesses, charities and public bodies run their email on Microsoft 365. Their mail goes through Microsoft’s filtering as well, and their IT team can add stricter rules on top. So when a quote, an invoice or a sales email “never arrived”, Microsoft is often where it went missing.
Quick check: sort your list by domain and add up the Microsoft ones. That tells you how much of your email (and your revenue) depends on getting this right.
First: junk or rejected?
These are two different problems. If your email bounces with an error like 550 5.7.515 Access denied, Microsoft is refusing it outright because authentication failed. Our guide to fixing 550 5.7.515 covers that. If the email arrives but lands in the Junk Email folder, Microsoft accepted it but didn’t trust it enough for the inbox. That’s what this checklist is for.
1. Authentication: SPF, DKIM and DMARC all passing and aligned
Since May 2025 Microsoft has required SPF, DKIM and DMARC from high-volume senders to Outlook.com, Hotmail and Live addresses. Even below that volume, mail that fails authentication is far more likely to be junked.
- Send a test to an Outlook.com address you own and check the headers for
spf=pass,dkim=passanddmarc=pass. - Make sure DKIM is signed with your domain, not your email platform’s. Why DKIM fails covers the usual causes.
- Check you have exactly one SPF record, within the 10-lookup limit.
2. Sending IP and domain reputation
Microsoft weighs the reputation of the IP address your mail comes from heavily. If you send from a dedicated IP, register it with Microsoft’s Smart Network Data Services (SNDS), which shows how Outlook.com sees that IP, including complaint rates and spam-trap hits. If you’re on a shared IP through an email platform, your platform manages this, but a sudden drop in placement across all your mail can point to a shared-IP problem worth raising with them.
Alongside SNDS, sign up to Microsoft’s Junk Mail Reporting Program (JMRP). It sends you a report each time an Outlook.com, Hotmail or Live user marks one of your emails as junk, so you can take them off your list before the complaints pile up. JMRP feeds are now linked to your SNDS account, and since early 2026 the reports no longer include the email body, so add a campaign reference to your headers if you want to know which send caused the complaint. On a shared IP, your email platform usually handles this for you.
Also check your domain and IPs against the main blocklists. A listing doesn’t always cause junking at Microsoft, but it’s a strong warning sign.
3. Complaints: people clicking “Report junk”
Every time an Outlook user marks your email as junk, it counts against you. Common causes:
- Emailing people who didn’t clearly sign up, or who signed up a long time ago and have forgotten you.
- An unsubscribe link that’s hard to find, so people report you as junk instead.
- Sending far more often than people expected when they signed up.
Microsoft expects a working unsubscribe link in marketing email (and one-click unsubscribe from bulk senders), so make it easy to find.
4. List hygiene
Repeatedly sending to addresses that don’t exist tells Microsoft you aren’t maintaining your list. Remove hard bounces straight away, stop mailing people who haven’t opened or clicked in six to twelve months (or send them a short re-engagement campaign first), and never buy or rent lists. Old Hotmail addresses that have been closed are a common source of both bounces and spam traps.
5. Consistent volume
Microsoft is suspicious of sudden spikes. If you normally send 2,000 emails a week and suddenly send 40,000 to your whole database, expect a lot of it to land in junk. Build volume up gradually, especially from a new domain or IP. This is called warming.
6. From and Reply-To addresses
Use a real, recognisable From name and an address on your own domain that can receive replies. A noreply@ address on a domain that doesn’t match your website looks less trustworthy to filters and to people.
7. Content and links
Content matters less than reputation, but it still counts:
- Avoid link shorteners and links to domains with poor reputation.
- Keep a sensible balance of text and images. A single large image with little text is a classic spam pattern.
- Make sure the domains in your links match the brand sending the email.
8. Engagement
Microsoft, like Gmail, notices whether people open, reply to and move your emails out of junk. Ask new subscribers to add you to their contacts, and focus regular sends on people who engage. Sending less to unengaged contacts often improves placement for everyone else.
Test before you guess
The quickest way to see where you stand is an inbox placement test: you send your campaign to a set of test mailboxes across Outlook, Hotmail, Gmail, Yahoo and corporate Microsoft 365, and see exactly where it lands. It turns “I think we’re going to junk” into a clear answer, and shows whether the problem is Microsoft-specific.
Find out why you’re landing in junk
Our deliverability audit runs inbox placement tests across Outlook, Hotmail, Gmail and Microsoft 365, checks your authentication and reputation, and gives you a prioritised list of fixes. Or start by checking your domain’s records free.
