Microsoft 365 network connectivity test fails

When the Microsoft 365 network connectivity test fails, it usually means there’s a problem somewhere between your device, your local network, and Microsoft’s cloud. A failed test means something is blocking or disrupting the connection, and fixing it is key to getting reliable access to Microsoft 365 apps again. These failures can slow down your work, so finding the cause quickly really matters.

Most of the time, these issues come from DNS hiccups, proxy settings gone wrong, or restrictions that keep Microsoft 365 from talking to the cloud the way it should. If you know the usual trouble spots and how to dig into them, you can cut down on downtime and keep things running.

Every business network has its quirks, so solutions aren’t always one-size-fits-all. That’s where professional support really comes in handy. If you need expert help, just reach out. You can find more about what we do at NetTech Consultants – IT Support and Managed IT Services in Jacksonville.

Common Causes of Microsoft 365 Network Connectivity Test Failures

When you run the Microsoft 365 network connectivity test and it fails, the issue usually lives in your local network settings, security gear, or how your traffic takes its path to Microsoft. Most failures point to misconfigurations that end up blocking or delaying the connection to Microsoft’s global network.

Incorrect Proxy or Firewall Configuration

We run into a lot of test failures because proxies or firewalls just aren’t set up right for Microsoft 365. Plenty of organizations treat Microsoft 365 traffic the same as any other internet traffic, which piles on extra checks and blocks services that need to work.

Microsoft 365 relies on a constantly changing list of endpoints. If your firewall or proxy doesn’t allow the right domains and IPs, you’ll see failures in your test results. Updating your rules with Microsoft’s published endpoint lists is a must.

TLS or packet inspection trips people up a lot, too. These tools matter for general web traffic, but when you use them on Microsoft 365, they can break authentication or slow down services like Teams. We suggest skipping deep inspection for trusted Microsoft 365 endpoints.

Key checks:

• Make sure firewall rules cover the latest Microsoft 365 URLs and IPs.
• Double-check proxy bypass settings for Microsoft 365 traffic.
• Turn off unnecessary TLS inspection for Microsoft 365 domains.

DNS Resolution Issues

DNS really matters for how quickly and accurately people connect to Microsoft 365. Slow or misconfigured DNS servers, or ones that point to far-off endpoints, can easily cause the connectivity test to fail.

We see a lot of setups where organizations still funnel DNS through a central office. This arrangement slows things down and can send traffic to Microsoft entry points that aren’t even close. Local DNS resolution gives better test results and a smoother user experience.

Old DNS records hanging around in caches can also cause problems. Devices might try to connect to endpoints that don’t exist anymore. Flushing caches regularly and using proper TTL settings helps keep things tidy.

Best practices:

• Use local DNS servers at branch offices.
• Check that DNS servers send users to the nearest Microsoft 365 entry point.
• Clear out stale DNS records and keep an eye on resolution times.

Port Restrictions and Blocked Endpoints

Microsoft 365 needs certain ports and endpoints open to work. If outbound ports like TCP 443 or UDP 3478–3481 are blocked, the connectivity test will fail. Services like Exchange Online, SharePoint, and Teams depend on these.

We come across a lot of firewalls set to only allow basic web browsing. That might seem secure, but it blocks Microsoft 365 from making the connections it needs. The test tool will flag these when it can’t reach the right ports or endpoints.

Some security appliances lump Microsoft 365 traffic in with everything else and restrict it. Using Microsoft’s endpoint web service to update your firewall and proxy rules helps keep the right doors open.

Checklist for port and endpoint access:

• Open TCP 443 for all Microsoft 365 services.
• Allow UDP 3478–3481 for Teams media traffic.
• Update firewall rules with Microsoft 365 endpoint data on a regular basis.

Troubleshooting Microsoft 365 Network Connectivity Test Errors

When the Microsoft 365 network connectivity test fails, it’s usually down to a configuration issue, browser oddity, or authentication snag. Tackling these areas step by step helps bring back reliable access to Microsoft 365 and makes your tests accurate.

SignalR Proxy Configuration Mismatches

We see failures pop up when network proxies block or mishandle SignalR traffic. Microsoft 365 uses SignalR for real-time communication, and a misconfigured proxy can mess with the test.

Common issues:

• Proxies that don’t allow WebSocket upgrades
• Wrong domain filtering for *.office.com or *.microsoft.com
• SSL inspection that interferes with encrypted traffic

To fix this, check that your proxies support WebSocket and SignalR. Make sure all domains in Microsoft’s official URLs and IPs are allowed. Disabling SSL inspection for trusted Microsoft domains usually clears up blocked upgrade attempts.

Try running the test on a direct internet connection, skipping the proxy. If it works, you’ll know the proxy is to blame and you’ll need to tweak its rules.

Web Browser Test Hang-Ups

The Microsoft 365 network connectivity test leans on your browser to run checks. If your browser hangs or doesn’t finish, it’s usually something about the browser settings or an extension.

Things to watch for:

• Browsers that are out of date and don’t support modern TLS
• Extensions that block scripts or change network requests
• Cached data that messes with the test

Try running the test in a supported browser like Microsoft Edge or the latest Chrome. Using InPrivate or Incognito mode rules out cached data and extensions.

If the test still gets stuck, clear the DNS cache on your computer and restart the browser. Testing on another browser or device can quickly show if the problem is local.

Authentication and Credential Problems

Connectivity tests can fail when something interrupts the sign-in process to Microsoft 365. This happens if cached credentials are wrong, multifactor authentication prompts don’t get through, or conditional access policies interfere.

Check these:

• Make sure the user signs in with valid Microsoft 365 credentials
• Confirm MFA prompts are delivered and not blocked by device settings
• Review any conditional access or security policies that might block the test

Clearing out stored credentials in Windows Credential Manager or starting with a fresh sign-in often stops authentication loops. If policies are the issue, adjust conditional access rules to let diagnostic traffic through.

Testing with a less restricted account can help figure out if the problem is policy-related or just tied to a specific user. This is especially handy in bigger organizations with lots of access controls.

Best Practices for Ensuring Reliable Microsoft 365 Connectivity

Getting reliable connections to Microsoft 365 comes down to good network configurations, accurate endpoint management, and using the right diagnostic tools. We focus on cutting latency, avoiding misconfigurations, and making sure traffic flows securely and efficiently to Microsoft 365.

Allowlisting Required Microsoft 365 Endpoints

One of the top steps: allowlist all required Microsoft 365 endpoints. Microsoft keeps these updated through the Microsoft 365 Endpoints web service, so firewalls, proxies, and other devices can grab the latest info. If you keep this list current, you’ll avoid service disruptions from outdated rules.

We always treat Microsoft 365 traffic differently than the rest of the web. That means skipping SSL or packet inspection for trusted Microsoft domains and IPs—those checks often slow things down or break services like Teams or Exchange Online.

Endpoints fall into Required, Optional, and Default. Our go-to move is to permit all Required endpoints across firewalls, DNS, and proxies. That way, authentication, data transfers, and real-time services stay stable.

Verifying Network and Device Settings

Even if you’ve got endpoints set up right, local network and device settings can still cause connectivity problems. We check that DNS resolution points users to the closest Microsoft entry point, not some faraway egress. Local DNS servers at branch offices help keep lookups fast.

We also make sure devices run the latest Microsoft 365 client versions. Old clients might not support new connectivity requirements. It’s worth checking network adapters, VPN clients, and proxies to make sure they don’t override local routing.

A common headache is sending Microsoft 365 traffic back through central offices when it’s not needed. Turning on local internet breakout lets users connect straight to Microsoft’s network. That shortens the route to services like SharePoint Online or Teams and really boosts performance.

Using Diagnostic and Troubleshooting Tools

When problems stick around, we turn to Microsoft’s official tools to figure out what’s going on. The Microsoft 365 network connectivity test checks latency, route efficiency, and overall connection health from wherever you’re testing. It’ll show if users connect to the closest Microsoft edge node or if something’s sending them on a weird detour.

We check out the connectivity.office.com portal too, since it gives a big-picture look at Microsoft’s network health across the globe. That way, we can tell if we’re dealing with a local setup issue or if something bigger is happening with the service itself.

For ongoing monitoring, it’s a good idea to add endpoint health checks to your current IT management tools. Regularly testing connections lets us spot routing changes or ISP hiccups before they mess with anyone’s workflow. This way, Microsoft 365 services stay up and running when people need them.