Outlook can’t send or receive emails in Office 365

Outlook in Office 365 sometimes just refuses to send or receive emails, and there are a bunch of reasons why. Maybe the network drops, the mailbox fills up, or something’s off in the account settings. If Outlook won’t deliver or receive messages, it’s usually because of a connectivity hiccup, a configuration slip, or some kind of account conflict. If you know where to look, you can usually get things back on track pretty quickly.

We work with businesses that rely on Outlook all the time, so we get how frustrating these issues can be. That’s exactly why we put together this guide. We’ll walk you through the most common causes, how to spot them, and some practical fixes that get email working again. Each section builds on the last, so you can start simple and work your way up to more advanced solutions without too much hassle.

Every business runs a little differently, though. If Outlook problems keep popping up or your team’s getting slowed down, let us know. NetTech Consultants – IT Support and Managed IT Services in Jacksonville can help with support that actually fits your organization.

Identifying Outlook Send and Receive Issues

When email suddenly stops moving in Microsoft Outlook on Office 365, it’s usually tied to specific error messages or symptoms that point to configuration, connectivity, or account problems. If you spot these signs early, you save yourself a lot of time and headaches.

Common Error Messages in Outlook

Outlook in Microsoft 365 throws out some pretty direct error codes or prompts when send and receive actions fail. You’ll usually see these in a pop-up or in the status bar at the bottom.

Here are some of the ones we run into most often:

• “Cannot connect to server” – usually means there’s a network or setup issue.
• “Enter your username and password” – often pops up if authentication fails or the password’s outdated.
• “Task reported error 0x800CCC0E” – typically points to wrong SMTP or IMAP settings.
• “Mailbox is full” – tells you the Microsoft 365 mailbox has hit its storage cap.

Each error nudges you toward a different fix. If you keep getting asked for your password, you probably need to update stored credentials. If it’s a server connection issue, you might need to check firewall or proxy settings. Pinning down the exact wording of the error helps you zero in on what’s really going on.

Typical Symptoms of Email Delivery Problems

Even when Outlook doesn’t show an error code, you can usually tell something’s up. One big clue: emails stuck in the Outbox. That usually means there’s a connection problem or the message is too big.

Other things to watch for:

• New emails aren’t showing up in the Inbox, even though you’re online.
• Messages take way longer to arrive than they should.
• Outlook keeps flipping into Work Offline mode.
• Sync errors pop up in the Send/Receive progress window.

In Office 365, these symptoms might also show up if you changed your account password but didn’t update it in Outlook, or if the Outlook profile got corrupted. If you pay attention to these patterns, you can figure out if the problem’s in the Outlook client, the account setup, or the Microsoft 365 service itself.

Troubleshooting Outlook Email Problems

When Outlook in Office 365 won’t send or receive emails, the problem usually comes down to connectivity, account settings, or the app’s overall health. If you check these areas carefully, you can usually figure out what’s wrong and fix it.

Check Internet Connection and Outlook Online Status

Start with the basics: make sure you’ve got a solid internet connection. Just open up a browser and try loading microsoft.com or another big site. If it won’t load, the network’s probably the culprit—not Outlook.

Outlook sometimes gets stuck in offline mode, which blocks mail syncing. In the Outlook ribbon, hit the Send/Receive tab and see if “Work Offline” is checked. If it is, switch it off and see if mail flow returns.

Check the Outlook status bar at the bottom, too. If it says “Disconnected” or “Trying to connect,” Outlook isn’t talking to Office 365 servers. Restarting Outlook or even rebooting your computer often fixes this if your internet’s working everywhere else.

Verify Account Settings and Server Configuration

Wrong account settings trip up a lot of users. In Outlook, go to File > Account Settings > Server Settings and double-check the incoming and outgoing mail server info against what Microsoft 365 or your provider says.

For Office 365, incoming mail should use IMAP with outlook.office365.com on port 993 (SSL on), and outgoing should be smtp.office365.com on port 587 (TLS on).

Make sure passwords are current. If you changed your password through the Microsoft 365 portal, you’ll need to update it in Outlook, too. Sometimes, you’ll need an app password instead of your regular one if you’re using a third‑party email client.

Keep an eye on mailbox size limits. Big attachments can block outgoing messages and leave them stuck in the Outbox. Shrinking files or using OneDrive links can help avoid this.

Update and Repair Outlook Application

If your connection and settings look good, Outlook itself might be the problem. Make sure you’re running the latest version—Microsoft 365 updates help keep things compatible and secure.

If Outlook’s still acting up, try the built‑in Repair Outlook tool. You’ll find it in Windows under Control Panel > Programs and Features > Microsoft Office > Change > Quick Repair. For stubborn issues, the Online Repair option reinstalls the main files.

Corrupted profiles or data files can also mess with send/receive functions. Creating a new Outlook profile and re‑adding your Office 365 account often clears things up. We also run the Inbox Repair Tool (scanpst.exe) to fix file corruption.

Staying on top of Outlook updates and repairs not only solves current issues, but it also helps prevent more email headaches down the road.

Resolving Profile and Security Conflicts

A lot of Outlook disruptions come from user profile problems or security software getting in the way. If you tackle these, Outlook can usually authenticate and talk to Office 365 without any trouble.

Fix Corrupted Outlook Profiles

A busted Outlook profile can keep accounts from syncing with Office 365. When this happens, you might see endless credential prompts, missing folders, or mail errors.

We usually check if the profile’s damaged. Making a new one is often the quickest fix. In Windows, go to Control Panel > Mail > Show Profiles > Add. Add the account again and set the new profile as default.

If you’ve got multiple accounts or local PST/OST files, back up your data before swapping profiles. Sometimes, the Outlook Profile Repair Tool or the built-in Account Repair option can fix things without needing a whole new profile.

Keep an eye on Outlook after repairing. If problems keep coming up, the data file itself might be corrupted, and you’ll need to rebuild the OST file or restore from backup.

Address Antivirus and Firewall Interference

Security software sometimes blocks Outlook from reaching Office 365. Antivirus email scanning can intercept messages and cause delays or connection errors. We suggest turning off just the email scanning feature and leaving real-time protection on.

Firewalls can also block Outlook from reaching Exchange Online servers. Make sure ports 443 (HTTPS) and 587 (SMTP) are open. Also, check that Outlook.exe isn’t being blocked by the firewall.

While troubleshooting, try disabling antivirus or firewall rules for a bit to test if Outlook connects. If it works, tweak the settings instead of leaving protections off. That way, you stay secure and keep Outlook sending and receiving as it should.

Advanced Solutions for Persistent Issues

If Outlook keeps failing to send or receive emails, sometimes the problem’s deeper than basic settings. At this point, we look at things like Exchange Online service health and the state of local mailbox storage or data files.

Exchange Online and Service Health Checks

In Microsoft 365, Exchange Online disruptions can directly mess with email. Check the Microsoft 365 Service Health Dashboard to see if there are any outages or degraded services. This saves you from wasting time troubleshooting your own setup if the problem’s actually in the cloud.

If the dashboard says everything’s fine, check your own tenant. Use the Exchange Admin Center to look at mail flow rules, connector status, and any throttling policies that might block or delay messages.

Verify DNS records like MX, SPF, and Autodiscover. Bad or outdated records can block Outlook from talking to Exchange Online. Testing mail flow with the Microsoft Remote Connectivity Analyzer gives you clear diagnostics.

By combining service health checks and tenant-level reviews, you can quickly tell if the problem’s on Microsoft’s end or if you need to tweak something in your Office 365 setup.

Managing Mailbox Storage and Data Files

Mailbox capacity can really mess with sending and receiving emails. In Office 365, if your mailbox hits its quota, you just can’t send or get messages until you free up some space. It’s a good idea to check mailbox usage in the Exchange Admin Center and clear out old or unnecessary stuff.

On your computer, Outlook data files like OST and PST sometimes get too big or even corrupted. Try running the Inbox Repair Tool (SCANPST.EXE) or just recreate the OST file—these steps usually fix sync problems.

Turning on Online Archiving or setting up retention policies in Microsoft 365 helps keep your main mailbox under control. This approach keeps things running smoothly and might even boost performance over time.

If you keep an eye on both your cloud storage and local files, Outlook tends to work better across all your devices.