Proxy authentication error 2606 means an app tried to connect through a proxy server and the proxy did not accept its login. The number 2606 is not an HTTP status code. The app that shows the message creates it. The standard HTTP code for the same problem is 407 Proxy Authentication Required.
Most people see "Proxy Authentication Error - 2606" or "Please check your proxy configuration and try again. [2606]" in Microsoft OneDrive, Outlook, or Teams on Windows. As of October 2026 we found no official Microsoft page that explains the code. The fixes below come from Microsoft's Q&A forum, other troubleshooting guides, and general proxy checks.
Quick fix for OneDrive or Outlook:
- Sign out of OneDrive or Outlook.
- Press Windows + R, run
RunDll32.exe InetCpl.cpl,ResetIEtoDefaults, and confirm the reset. Do not select the box to delete personal settings. - Open the app again and sign in.
Quick fix for a proxy you bought or set up: copy the credentials again from the provider dashboard, confirm the format your tool expects, and test one proxy with cURL before you import a full list.
Proxy authentication error 2606 in OneDrive, Outlook, and Teams
Users on Microsoft Q&A report the error when OneDrive tries to sync or when Outlook and Teams try to sign in. Many reports start after a password change. Some users see it only on a company network and not on VPN or at home. Others see the reverse and can sign in only with the VPN disconnected. Both patterns point to a proxy or VPN that rejects or alters the sign-in traffic.
Teams and OneDrive often fail together. A Microsoft Q&A thread from September 2025 suggests why: both use the same network and authentication path, so one blocked proxy breaks both.
Which fix to try first
| What you notice | Likely cause | Start with |
|---|---|---|
| Works on a phone hotspot, fails on the office network | Company proxy or firewall | Step 8, then IT |
| Started after a password change | Stale saved credentials | Step 5 |
| Started after you unlinked an account or switched networks | Leftover Internet Options or proxy settings | Steps 1 and 2 |
| Fails only while a VPN is on, or only while it is off | VPN or proxy conflict | Step 4 |
Work through the steps in order. Stop when the app signs in.
1. Reset Internet Options
This is the fix that most users on the Microsoft thread confirmed. The accepted answer, posted in February 2024, has over 100 helpful votes. Sign out of the app first. Then press Windows + R and run:
RunDll32.exe InetCpl.cpl,ResetIEtoDefaults
Leave "Delete personal settings" unselected, then apply the reset and restart the PC. The command resets the legacy Internet Options that Windows apps share. Microsoft has not said why it clears 2606, and reports differ on whether it touches proxy settings. Check step 2 even if the reset works. Open the app again and sign in.
2. Check the Windows proxy settings
In Windows 11, open Settings > Network & internet > Proxy. If you do not need a proxy, turn off "Use a proxy server" and any setup script. If you are not sure, turn on "Automatically detect settings". On a company device, do not change settings that your IT team set.
To read the same values from a command prompt without changing anything:
reg query "HKCU\Software\Microsoft\Windows\CurrentVersion\Internet Settings" /v ProxyEnable
reg query "HKCU\Software\Microsoft\Windows\CurrentVersion\Internet Settings" /v ProxyServer
reg query "HKCU\Software\Microsoft\Windows\CurrentVersion\Internet Settings" /v AutoConfigURL
ProxyEnable set to 0x1 means a manual proxy is on. A ProxyServer value shows its address. AutoConfigURL shows a setup script. If a proxy shows up that you did not set, a VPN client, security software, or a policy may be adding it.
3. Check the WinHTTP proxy
Windows keeps more than one proxy setting. Apps that use the browser stack read the settings above. Some services use a separate system proxy called WinHTTP. Open Command Prompt and run:
netsh winhttp show proxy
"Direct access (no proxy server)" means no WinHTTP proxy is set. If a proxy is listed and you do not expect one, ask your IT team before you change it.
4. Turn off VPN, proxy, or firewall software for a test
A Microsoft moderator on the thread suggested this. If the error stops, that software is changing or blocking the sign-in traffic. If it only works with the VPN disconnected, sign in first and connect the VPN afterwards.
5. Clear stored credentials
A saved password that no longer matches is a common trigger after a password change. Open Control Panel > Credential Manager > Windows Credentials. Remove the entries for OneDrive, Microsoft Office, or your proxy host, then restart the app and sign in again. Removing credentials makes Windows ask for them again, so have your password ready.
6. Unlink and reset OneDrive
In OneDrive, open Settings > Account and select "Unlink this PC". Then press Windows + R and run:
%localappdata%\Microsoft\OneDrive\onedrive.exe /reset
If OneDrive does not start again after a few minutes, open it from the Start menu and sign in. Microsoft states that a reset does not delete your files.
7. Reset the network stack
If the steps above fail, run these in an administrator Command Prompt, then restart:
netsh int ip reset
netsh winsock reset
ipconfig /flushdns
These commands reset network configuration for the whole PC. Do not run them on a managed device without IT approval.
8. Test another network, then ask your IT team
Connect the PC to a phone hotspot and sign in. If it works there, the office network or its proxy is the problem, and no local fix will hold. Tell IT whether other users see the same error. They may need to update your proxy credentials or allow Microsoft 365 traffic. Microsoft publishes the Microsoft 365 URLs and IP address ranges that a proxy should let through, including a JSON feed and PAC files.
If the sign-in still fails, remove and re-add the account under Settings > Accounts > Access work or school, or run a Quick Repair of Microsoft 365 from Settings > Apps > Installed apps.
Error 2606 in proxy tools, bots, and browser profiles
If a scraper, bot, browser profile tool, or proxy checker shows an authentication error with a code like 2606, the code comes from that tool. Check the tool's documentation for its exact meaning. The cause is almost always the same class of problem: the proxy rejected your credentials, your source IP, or your session settings.
Start with the basics:
- Copy the proxy credentials again from your provider dashboard.
- Confirm the format your tool expects:
host:port:username:password,username:password@host:port, or separate fields. - Check that the port matches the proxy product and protocol.
- Remove extra spaces, quotes, hidden characters, and line breaks.
- Confirm your plan is active and has traffic or IPs left.
- If your account uses IP allowlisting, add the public IP of the machine that runs the tool.
- Test one proxy with cURL before you import a full list.
- If the username includes country, city, or session parameters, remove them and test again.
If one clean proxy works, the provider is fine. The problem is usually one malformed line, an unsupported parameter, or a format mismatch.
Common causes of proxy authentication failures
| Cause | What to check |
|---|---|
| Wrong proxy format | Your tool may expect separate host, port, user, and password fields |
| Copied spaces or hidden characters | Copy the proxy line into a plain-text editor and check it |
| Wrong protocol or port | HTTP and SOCKS5 ports are often different |
| Expired or inactive plan | Confirm plan status, traffic balance, and billing |
| IP allowlist mismatch | Add your current public IP or use username and password auth |
| Bad geo or session parameter | Remove country, city, or sticky-session flags and test again |
| Password changed | Copy the new credentials from the provider dashboard |
| Tool parser issue | Try another format, separate fields, or URL-encoded credentials |
Do not rotate through hundreds of proxies while the base credential is wrong. Every line fails for the same reason, and the logs get harder to read.
Check the proxy format first
Different tools want different layouts:
host:port:username:password
username:password@host:port
http://username:password@host:port
socks5://username:password@host:port
Some browser profile tools use four separate fields:
Host: proxy.example.com
Port: 12345
Username: customer-zone-us-session-abc
Password: your-password
If you paste the full proxy line into the host field, authentication fails. If the tool expects user:pass@host:port and you import host:port:user:pass, the parser can read the username as part of the host. Our proxy format converter changes a list from one layout to another.
Test with cURL
A cURL test shows whether the credentials work outside your main tool:
curl -v -x "http://username:password@host:port" https://ipinfo.io/ip
For a SOCKS5 proxy:
curl --socks5 "host:port" --proxy-user "username:password" https://ipinfo.io/ip
A working proxy prints the exit IP. A login problem usually shows 407 Proxy Authentication Required in the verbose output, or a connection error. If you use Python, our guide to Python Requests proxy authentication shows how to pass proxy credentials in code.
If cURL works but your bot or browser profile fails, the problem is the tool's format, protocol choice, or handling of special characters.
Watch for special characters in credentials
Passwords that contain @, :, /, #, ?, or & can break a proxy URL. This line is ambiguous:
http://user:p@ss:word@host:port
The tool cannot tell where the password ends and the host starts. Use separate username and password fields if the tool has them. If it needs one URL, URL-encode the reserved characters, for example @ becomes %40. You can also set a simpler password if your provider allows it.
Check IP allowlisting
Some proxy accounts support two login modes: username and password, or IP allowlist. In allowlist mode, the proxy rejects any source IP that is not on the list, even when the username and password are correct.
Check the public IP of the machine that runs the tool:
curl https://ipinfo.io/ip
Compare it with the allowlist in your provider dashboard. If the tool runs on a VPS, a cloud runner, or a remote desktop, allowlist that machine's IP, not your home IP.
Check plan, balance, and product type
Authentication can also fail when the account exists but the requested product is not available. Check that:
- The subscription or balance is active.
- The plan has traffic or IPs left.
- You use the correct hostname and port for residential, ISP, or datacenter access.
- The requested country, state, or city is in the plan.
If you are not sure which proxy type fits your task, read datacenter proxies vs residential proxies and ISP proxies vs residential proxies.
Session parameters can break authentication
Residential proxy usernames often carry routing options such as country, city, or session ID:
customer-abc-country-us-session-profile1
One wrong country code, delimiter, or session syntax can make the gateway reject the whole login. Start with the plain username from your provider. When that works, add parameters one at a time. Our guide on how to use residential proxies covers sticky and rotating sessions.
Authentication errors vs. target blocks
Proxy login errors and website blocks can look alike inside one automation tool.
| Symptom | More likely issue |
|---|---|
| Error appears before any page loads | Proxy authentication |
| cURL through the proxy fails | Proxy credentials, plan, or allowlist |
| Proxy checker says auth failed | Proxy credentials or format |
| Target returns 403 after proxy connects | Target access policy or IP reputation |
| Target returns 429 after proxy connects | Rate limit or request pacing |
| Only one website fails | Target-specific block |
| Every request through the proxy fails | Proxy setup or account access |
If the proxy connects and the site then blocks you, read our guides to HTTP 403 Forbidden or HTTP 429 Too Many Requests, depending on the response. If the proxy never accepts the login, stay focused on credentials.
FAQ
What is Microsoft proxy authentication error 2606?
It is an error that OneDrive and Outlook show when a proxy rejects their sign-in traffic. Microsoft has not documented the code. Users on Microsoft Q&A fixed it by resetting Internet Options, checking Windows proxy settings, or resetting OneDrive.
Is proxy authentication error 2606 the same as HTTP 407?
Not exactly. HTTP 407 is the standard response a proxy sends when it needs credentials. Error 2606 is an app's own code, but it points to the same class of problem.
Why does one tool work but another shows error 2606?
The tools may parse proxy strings differently. One may expect host:port:user:pass, another user:pass@host:port or separate fields. They can also handle special characters in passwords differently.
Should I rotate proxies after error 2606?
No. Fix authentication first. More proxies do not help if the username, password, port, allowlist, or plan is wrong.
How do I fix proxy authentication error 2606 in OneDrive?
Sign out, run RunDll32.exe InetCpl.cpl,ResetIEtoDefaults with "Delete personal settings" unchecked, restart, and sign in again. If that fails, turn off any proxy or VPN, clear stored credentials, and test on another network.
Does error 2606 also affect Teams and Outlook?
Yes. Users report 2606 in Teams, Outlook, and OneDrive. They share the same network and sign-in path, so a proxy that rejects one usually rejects the others.
Is it safe to run ResetIEtoDefaults?
It resets legacy Internet Options, so you may lose custom security zones, saved form data, or proxy-related settings. Leave "Delete personal settings" unchecked. On a company PC, ask IT first, because some settings come from policy.
Final thoughts
Decide first where the error comes from. If it is OneDrive, Outlook, or Teams, work through the Windows steps, and test on a hotspot early, because that tells you whether the network is at fault. If it is a proxy tool, test one proxy with cURL and compare the format, port, and allowlist before touching anything else. This matters for checkout bots and monitors on ticketing and retail sites, where one bad credential line fails every task. Once the login works, residential proxies suit rotating or sticky sessions, and ISP proxies suit tasks that need static IPs.