Why Do My Emails Go to Spam in Outlook but Not Gmail?

The same newsletter lands in Gmail’s inbox and Outlook’s junk folder. Same message, same day, same list. Gmail readers open it. Outlook readers say it never came. Every dashboard you check shows green.

Here is the short answer. Gmail and Microsoft judge your mail separately, so a clean report from one says nothing about the other. When only Outlook junks your mail, the most common cause is your sending IP address, which Microsoft cares about more than Gmail does. The fastest checks: a blocklist check on the IP you send from, and Microsoft’s free SNDS page. The rest of this article walks the causes and the fixes.

Gmail and Outlook keep separate scorecards

Two filters. Two histories. Two verdicts. Google builds its opinion around your domain: the reputation graphs in Google Postmaster Tools, whether people open and reply to your mail, and your email records. Microsoft runs a different system. It leans on your sending IP address, and it reports through pages most senders never open.

Microsoft also got stricter. On May 5, 2025 it began enforcing rules for big senders: 5,000 or more emails a day to Outlook.com must pass SPF, DKIM and DMARC. Failures got temporary errors at first. Now they can get outright rejections, like 550 5.7.515 Access denied. Microsoft announced this on its Tech Community blog. These checks are the minimum. Where your mail lands is decided above them, by signals the two providers weigh differently.

Do this: prove the gap is real before you change anything. Send one test to an Outlook.com address you own and one to Gmail. A confirmed split puts you in this article. Both going to junk puts you in the spam diagnostic hub instead.

The three causes, ranked

Cause one: your sending IP has a bad record

The most common answer. Your email leaves from an IP address, the number that identifies the mail server. On a sending platform, that IP is often shared with its other customers. Microsoft keeps a record for that IP: complaints, spam trap hits, what everyone on it has sent. A neighbour’s bad sending can sink your mail at Outlook.

Gmail pays less attention to the IP and more to your domain. So the split in the title happens: your domain is clean, your records pass, and Outlook still junks you.

The tell: run the blocklist checker on the sending IP, not just your domain. Find the IP in the first Received: line of a message you sent, visible in the header analyzer. A listed IP, or listings that come and go across weeks, is your answer.

What to do: on a shared pool, ask your platform about the pool’s standing and about a dedicated IP. If the IP is yours and listed, fix the cause first, then request removal at Microsoft’s sender portal, sender.office.com. Removal without the fix earns a relisting, usually fast.

Cause two: complaints you cannot see

Gmail gives every sender Postmaster Tools, with a spam-rate graph against the 0.3 percent line. Microsoft has the same kind of data, but you must ask for it.

Microsoft’s complaint program is JMRP, the Junk Mail Reporting Program. When an Outlook user clicks “junk”, JMRP can forward that message to you. Without it, a complaint spike at Microsoft is invisible. No dashboard shows it. The first sign is your mail landing in junk. The August 5 post on Gmail and Yahoo sender requirements explains the complaint limits. Microsoft holds you to the same 0.3 percent line, but tells you about it far less.

The tell: sign up for JMRP. It is free. If reports start arriving, you have been collecting complaints you never saw, and the messages show you which campaign drew them.

What to do: read what the complaints name. It is usually one segment, one old list, or one campaign. Cut it, and the complaint rate recovers with the next sends.

Cause three: Microsoft’s filter flagged the content or links

The least common cause, but real. Microsoft’s filter, SmartScreen, judges content and links its own way. A shared link shortener, a redirect through a flagged site, or an attachment type Microsoft distrusts can tip one message at Outlook while Gmail does not mind.

The tell: the split survives a fresh test with clean records, an unlisted IP, and a quiet JMRP. That leaves the message itself. Swap the link domain, or send a version without the link, and watch where it lands.

What to do: drop shared shortener domains, link from your own domain, and keep heavy attachments out of first-contact mail. This is the only cause a content change fixes. Do not rewrite a template for the other two. It will not help.

How to see what Microsoft thinks of you

Microsoft shows its view of your sending through two free portals, and both ask for your sending IP:

• SNDS, the Smart Network Data Service. Complaint rate, trap hits and volume per IP, as Microsoft sees it. This is the closest thing Microsoft has to Postmaster Tools, and it shows current data only. No history.
• JMRP, the Junk Mail Reporting Program. The complaint loop from cause two. SNDS shows the rate. JMRP shows the actual messages.

Both are free with a Microsoft account, and both are keyed to the IP. That alone tells you where Microsoft’s attention lives. A SaaS or transactional sender on a shared pool may not control the IP at all, and that is a clue in itself: if you cannot see the IP’s standing, you cannot check cause one by hand.

Do this: register both. Then look at SNDS after each campaign for a month. Those screenshots become the “before” picture you will want when a real problem lands.

Verify the fix took

Run the email health check on your sending domain and fix anything it flags. Every cause above gets worse on top of a broken record. Then test against reality: send to a real Outlook.com address and look in the junk folder yourself. That is the only test that answers the question without waiting for a customer.

What checking by hand misses

Every check above answers for one day. The Outlook side is the least watched part of email, because most senders learn Microsoft’s opinion from a reader. SNDS shows only the present. An IP listing can start on a Tuesday and clear by Friday, taking that week’s mail with it, and a hand check on Sunday never sees it. A complaint spike builds in silence for exactly as long as JMRP stays off.

That silence is what LitInboxes watches. It re-checks your records, blocklists and reputation signals every six hours. It keeps dated history that turns a slow problem into “the IP was listed on the 12th”. And it alerts you when something moves: email on every plan, Slack, Discord or webhook on Pro. There is a live demo if you want the view before the next Outlook reader goes quiet.

The checklist

1. Send one test to a real Outlook.com address and one to Gmail. Confirm the split is real.
2. Run the email health check and fix every record it flags.
3. Find your sending IP in the first Received: line and run the blocklist checker on it.
4. If it is listed, fix the cause, then submit one removal request at sender.office.com.
5. Register SNDS and JMRP. Read what the first JMRP reports name.
6. Cut the segment or campaign the complaints point at.
7. Retest with a real Outlook address and check the junk folder yourself.
8. Put the domain and IP on a watch cycle, weekly by hand or with continuous monitoring, so the next Microsoft-side change announces itself.