1. Check webmail first: is it Outlook or your account?
Open a browser and sign in to your email online. For Microsoft 365 business accounts that's outlook.office.com, and for personal Outlook.com and Hotmail accounts it's outlook.live.com. Send yourself a test email.
- Webmail works: your account is fine and the problem is the Outlook app on your computer. Continue from step 2.
- Webmail doesn't work, or you can't sign in: the problem is your account. Skip to step 7.
2. Make sure Outlook isn't offline
In classic Outlook, look at the bottom status bar. If it says Working Offline or Disconnected, go to the Send / Receive tab and click Work Offline to toggle it off. Also confirm the computer itself is online by loading a website.
3. Clear a stuck email from the Outbox
One email with a large attachment can block everything behind it. Open the Outbox folder. If an email has been sitting there, drag it to Drafts, remove or shrink the attachment, and try again. As a rule of thumb, attachments over about 20 MB often fail, depending on your email service and the recipient's. Share large files as a OneDrive or SharePoint link instead.
4. Restart Outlook, then your computer
Close Outlook completely. If it's frozen, end it from Task Manager (Ctrl + Shift + Esc), then reopen it. If that doesn't help, restart the computer.
5. Start Outlook in Safe Mode
Add-ins are a common cause of crashes and sync problems in classic Outlook. Press Windows + R, type outlook.exe /safe and press Enter. If Outlook works in Safe Mode, go to File → Options → Add-ins and disable add-ins one at a time until you find the culprit.
6. Repair Office or create a new Outlook profile
- Repair Office: Settings → Apps → Installed apps → Microsoft 365 (or Office) → ⋯ → Modify → Quick Repair. If that doesn't work, try Online Repair.
- New profile: a corrupted profile is a very common cause of stubborn problems. Close Outlook, open Control Panel → Mail (Microsoft Outlook) → Show Profiles → Add, set up your account in the new profile, and set it to be used by default.
7. If webmail is broken too
- Password changed recently? Outlook may be waiting for you to sign in again. Look for a sign-in prompt hidden behind other windows.
- Mailbox full? Check your storage in webmail settings. A full mailbox stops new email arriving. Empty Deleted Items and archive old mail.
- Service outage? Check Microsoft's service status, or ask your IT provider. Business admins can see service health in the Microsoft 365 admin centre.
- Can't sign in at all, or see strange sent emails? Your account may be compromised. See our guide on what to do if you've clicked a scam link and act quickly.
8. Emails sending but bouncing back
If your emails send but come back with an error, or customers say your emails land in their junk folder, the cause is often your domain's email security records (SPF, DKIM and DMARC) or a mailbox that's been flagged for spam. These are configuration problems, not Outlook problems, and need fixing at the domain and Microsoft 365 level.
When to get help
- Email works in webmail but Outlook still won't sync after a repair and new profile.
- Emails are bouncing, or customers aren't receiving them.
- You suspect someone else has access to your mailbox.
- You're moving email to Microsoft 365 and don't want to lose anything.
We set up, migrate and secure Microsoft 365 for small businesses, including the SPF, DKIM and DMARC records that keep your emails out of junk folders.
Quick answers
Why are my emails stuck in the Outbox?
Usually because Outlook is offline, a large attachment is blocking the queue, or Outlook needs to sign in again. Check Work Offline, move the stuck email to Drafts and restart Outlook.
How do I know if the problem is Outlook or my email account?
Sign in to webmail in a browser. If email works there, the problem is the Outlook app on your computer. If it doesn't, the problem is your account, password, storage or the email service.
Why do my emails go to other people's junk folders?
Often because the domain's SPF, DKIM or DMARC records are missing or wrong. These need to be configured correctly for your domain and email service.