Outlook not receiving emails: find the cause, in order

If Outlook has stopped receiving email, the cause is usually one of three things: the message was filtered into junk or quarantine before you saw it, a rule moved or forwarded it, or the mailbox has hit its size limit and is quietly refusing new mail. All three are common, all three are fixable, and none of them is helped by restarting Outlook. This is the order we work through them in, cheapest and most likely first, so you find the actual cause rather than trying things until something changes.

Last updated 14 August 2026. We review this guide every six months, and after any significant change to the Microsoft 365 admin centre.

Some of this needs administrator access, so it is worth knowing which parts before you start. You can do steps 1 to 5 yourself with no special rights. Steps 6 to 10 need someone with Microsoft 365 admin access: licences, mailbox size, account level forwarding, mail flow rules, message trace and DNS all sit behind it, as does releasing anything quarantined as high confidence phishing or malware. If you are not that person, get them involved early rather than nine steps in.

1. Check webmail first, before anything else

This takes thirty seconds and it halves the problem, which makes it the most valuable thing on this page. Sign in to your mail in a browser at outlook.office.com and look for the missing message there.

If the missing mail is in webmail, your mailbox is working perfectly and the fault is the Outlook program on that one computer. That is a much smaller problem: a sync issue, a corrupted local profile, or a filtered view. If the missing mail is not in webmail either, then it never arrived or it was moved or blocked at the mailbox level, and nothing you do inside the Outlook program will bring it back. Everything below assumes you have done this test, because it decides which half of the problem you are in.

2. Work out whether it is one person or everyone

The second question is scope, and people skip it constantly. Ask whether anyone else is missing mail today.

One person means the cause is nearly always that mailbox or that computer: a full mailbox, a rule, a licence change, a local profile. Several people at once means something central changed, and that is a completely different search: DNS, a mail flow rule, a licence batch, or a service issue at Microsoft's end. The mistake worth avoiding here is chasing a central problem one desk at a time. If three people stopped receiving mail this morning, do not rebuild three Outlook profiles.

3. Look in the places mail actually hides

Before assuming the message never arrived, check where it might have landed instead. In order of how often it turns out to be the answer:

• Junk Email. The obvious one, and still the most common.
• The Other tab. If Focused Inbox is switched on, real mail regularly ends up under Other, and people who do not know the tab exists never look.
• Archive and Deleted Items. Usually a rule, or a phone that archived it with a stray swipe.
• Notes and RSS Subscriptions. If mail is landing in either of these, stop and read step 5. Microsoft lists rules that move mail to Notes, Junk Email or RSS Subscriptions as a recognised sign of a compromised account, because they are folders nobody ever opens.

Search is worth using properly here too. Search the whole mailbox rather than the inbox, and search on the sender's address rather than the subject, because subjects get changed and addresses do not.

4. Check quarantine

Quarantine is the layer above junk, and it is where mail goes when Microsoft 365 thinks it is dangerous rather than merely unwanted. It is a genuinely common cause of a message that a sender swears they sent and you never saw, because unlike junk, nothing appears in your mailbox at all.

Quarantined mail lives in the Microsoft Defender portal at security.microsoft.com, under Review and then Quarantine. You can view and release your own messages that were caught as spam, high confidence spam, bulk, phishing, or spoofing and impersonation attempts.

There are two things you cannot release yourself, and this is where people get stuck: high confidence phishing and malware can only be released by an administrator, as can anything quarantined by a mail flow rule. If the message you want is one of those, you need an admin, and it is worth them looking at why it was caught before releasing it.

5. Check rules and forwarding, and know what a bad finding looks like

Rules are the single most common reason mail "disappears" while everything else looks healthy. A rule can move a message, delete it, or forward it somewhere else, and it does so silently and permanently. Check the rules on the mailbox, both the ones set in Outlook and any forwarding set on the account itself, which a user cannot see from their own Outlook.

Most of the time you will find something innocent: a rule someone wrote three years ago to tidy a project that finished, filing mail into a folder they stopped opening. Fix it and move on.

But if you find a rule you cannot account for, especially one forwarding mail to an outside address, stop treating this as an email problem. An unexplained forwarding rule is one of the recognised signs of a compromised mailbox, and it is the mechanism behind invoice redirection fraud: the attacker keeps a copy of your mail flowing to themselves, watches for an invoice, and steps in with changed bank details at the right moment. Deleting the rule and carrying on is the worst possible response, because it removes the evidence and leaves whoever set it still holding the account.

If that is what you have found, the mailbox needs proper incident handling rather than a settings change. In order: reset the password, and do not send the new one to the affected mailbox, because the attacker may still be reading it. Revoke the account's active sessions, because a password reset on its own does not sign an attacker out of a session they already hold. Check multi factor authentication is on and that no unfamiliar method was added. Review which applications have been granted access to the account, since consent to a malicious app survives a password change. Then look through Sent Items and Deleted Items to work out what was sent and what was read, because that determines who you need to warn.

That last part matters more than it sounds. If invoices went out from a compromised mailbox, your customers may be about to pay someone else. We have written about how that scam works in the fake invoice and payment redirection scam, and the broader protections in cyber security for small business.

6. Check whether the mailbox is full

A full mailbox is an unglamorous cause that catches a lot of people, partly because of how it fails. It does not stop dead. It keeps accepting mail for a while, then starts refusing it, and senders begin getting bounce messages while the mailbox owner notices nothing except that it has gone quiet.

The current limits are worth knowing, because "my mailbox is huge" is usually a guess:

If a shared mailbox is the one that has gone quiet, check its size before anything else, because 50 GB is easier to reach than people expect on an address that has been collecting mail for a decade. There is more on that in our guide to shared mailboxes.

7. Check the licence and the mailbox state

This one is quick to check and embarrassing to miss. In the Microsoft 365 admin centre, under Users and then Active users, confirm the person still holds a licence that includes Exchange Online.

Licences get removed by accident during a tidy up, or lapse when a card expires, and the mailbox stops receiving mail. The reason this is worth checking rather than assuming: after a licence is removed the mailbox is retained for 30 days, so it looks like it still exists while behaving as though it does not. If someone has left recently and their address is still meant to receive mail, converting the mailbox to a shared mailbox is usually the right answer rather than paying for a licence indefinitely.

8. Check the domain's MX records

If nothing from outside your company is arriving at all, while internal mail moves normally, that pattern points hard at DNS. MX records tell the rest of the world where to deliver mail for your domain, and if they are wrong, mail is going somewhere else entirely and no work inside Outlook will ever find it.

This tends to happen after a website move, a change of hosting provider, or a domain that lapsed and was renewed with default records. The internal and external split is the clue: internal mail never leaves Microsoft 365 and so keeps working, which makes the problem look stranger than it is. Confirm the MX records point at Microsoft 365, and while you are there, check the domain has not quietly expired.

9. Check mail flow rules

Mail flow rules, sometimes still called transport rules, run across the whole organisation in the Exchange admin centre. They are powerful, they are invisible to users, and they are usually written once during a specific problem and never looked at again.

The classic failure is a rule that was correct when written and is now much broader than intended: something set up to redirect mail from a departing staff member, or to block a nuisance sender, that now catches far more than it should. Because these rules apply to everyone, this is worth checking early when several people are affected and late when only one person is.

10. Run a message trace for the definitive answer

Everything above is a reasonable guess. A message trace is the actual answer, which is why an IT provider goes here early rather than last.

In the Exchange admin centre, under Mail flow and then Message trace, search for messages between the sender and the recipient over the relevant dates. The trace tells you whether the message reached Microsoft 365 at all, and if it did, exactly what happened to it: delivered, filtered as spam, quarantined, caught by a rule, or expanded to a different address. That single result usually ends the conversation, because it separates the two situations that look identical from the inbox: the sender never actually sent it, and it arrived and was moved.

If the trace shows nothing at all for a message a sender insists they sent, the problem is on their side or in DNS, and you have just saved yourself from searching a mailbox that never received anything.

If mail is arriving but going to junk on the way out

One pattern worth separating out, because it gets misdiagnosed as a receiving problem: if people tell you they replied and you never got it, and your own mail to customers keeps landing in their junk, that is an authentication problem rather than a delivery one. The records that prove your mail is genuinely yours are SPF, DKIM and DMARC, and when they are wrong, mail in both directions starts behaving oddly. That is covered properly in why your business email lands in spam, and if senders are getting bounce messages, the code in the bounce tells you exactly what went wrong in how to read an email bounce back.

FAQ

Why is Outlook not receiving emails but I can send them?

Sending and receiving fail for different reasons, so working in one direction only is a useful clue rather than a puzzle. If you can send but not receive, the mail is usually being stopped or moved after it arrives, by junk filtering, quarantine, or a rule, or it is not arriving at all because the domain's MX records point somewhere else. Check Outlook on the web first. If the missing mail is not there either, the problem is at the mailbox or DNS level rather than in the Outlook program.

Why has Outlook stopped receiving emails suddenly?

A sudden stop usually means something changed, rather than something broke slowly. The common causes are a mailbox that has just reached its size limit, a licence that lapsed or was removed, a rule or forward that was added, a DNS or domain renewal change, or a new mail flow rule. If it stopped for several people on the same day, look for a central change first, because chasing it computer by computer will waste the afternoon.

Do I need admin access to fix Outlook not receiving emails?

Not for all of it. You can check webmail, your own junk and hidden folders, your own rules, and release most of your own quarantined mail without any admin rights. You will need a Microsoft 365 administrator for licences, mailbox size, forwarding set at the account level, mail flow rules, message trace, DNS records, and for releasing anything quarantined as high confidence phishing or malware. It is worth knowing that early, so you do not work nine steps into a fix you cannot finish.

I found a rule forwarding my email to an address I do not recognise. What should I do?

Treat it as a security incident, not a settings mistake. An unexplained forwarding rule is one of the recognised signs of a compromised mailbox, and it is how invoice redirection fraud usually works. Deleting the rule and carrying on leaves whoever created it still holding the account. The account needs its password reset, active sessions revoked, multi factor authentication checked, connected apps reviewed, and the sent and deleted items examined to see what was taken or sent. Do not send the new password to the affected mailbox.

Why is one person not receiving email when everyone else is fine?

When it is one person, the cause is nearly always specific to that mailbox or that computer, so start there rather than with the mail system. The usual suspects are a full mailbox, a rule that person or someone else added, a licence change, junk filtering of one particular sender, or a local Outlook profile that has gone wrong. If it is one person and one sender only, look at filtering and blocked sender lists before anything else.

Can Alien IT sort out email that has stopped working?

Yes. Mail that has stopped arriving is one of the most common things we get called about, and it is usually solved the same day once someone can see the message trace and the account settings. If the cause turns out to be a compromised mailbox we will handle it as a security incident and tell you plainly what happened and what was exposed. If you would rather not work through the steps yourself, that is a perfectly reasonable place to hand it over.

The bottom line

Check webmail first, because it tells you whether you are fixing a computer or a mailbox. Then establish whether it is one person or everyone, because that decides whether you look local or central. Most cases end in junk, quarantine, a rule, or a full mailbox. The ones that do not are usually a licence or a DNS change, and a message trace will settle any argument about whether a message ever arrived. The one finding that changes the nature of the job is a forwarding rule nobody can account for, because that is not a misconfiguration, it is someone else in the account.

Email stopped and you would rather it was just fixed? We do this most weeks, usually same day, and we will tell you what actually caused it. Tell us what is happening and we will take it from there.