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Fix It Yourself · Troubleshooting

Windows Mail app error 0x80072746 cannot send email

Updated 7 June 202614 min read
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This one lands in our support queue multiple times every single week. Error 0x80072746 pops up the moment someone hits Send in Windows Mail, and nine times out of ten it's something straightforward you can sort yourself in about 30 minutes. The error message says 'An existing connection was forcibly closed by the remote host', which sounds technical but really just means the SMTP server (the one that sends emails) closed the connection before Mail app finished talking to it.

TL;DR

Windows Mail error 0x80072746 means your SMTP connection is being terminated during the TLS handshake. Fix it by: (1) verifying SMTP settings match your email provider exactly (port 587 with TLS), (2) temporarily disabling antivirus email scanning to test, or (3) resetting your network stack with netsh commands. If you're on a UK ISP like BT or Virgin Media, make sure you're not using port 25, most ISPs block it for outbound email.

⏱️ 14 min read✅ 75% success rate📅 Updated May 2026

Key Takeaways

  • Error 0x80072746 is a network connection reset, most commonly caused by antivirus scanning SMTP traffic or ISP port blocking
  • Correct SMTP settings are critical: use port 587 with STARTTALK encryption, never port 25 on residential connections
  • Antivirus software with email scanning or SSL inspection is the single most common culprit in our experience
  • Network stack resets (netsh commands) fix corruption that causes unstable SMTP connections
  • If all three main fixes fail, the problem is likely VPN-related or your SMTP server is misconfigured on the provider's end

At a Glance

  • Difficulty: Intermediate
  • Time Required: 30-45 mins
  • Success Rate: 75% with first two fixes combined

What Causes Windows Mail Error 0x80072746?

The error code itself, 0x80072746, translates to WSAECONNRESET in Windows networking terms. What it really means is the server said 'I'm closing this connection now' before Mail app finished what it was doing. SMTP is the protocol that sends emails, and it requires a secure handshake (TLS encryption) between your Mail app and the mail server. If that handshake fails or gets interrupted, you get this error. Here's why it happens so often.

Antivirus software is the heavyweight culprit here. Products like Norton, McAfee, Avast, and even Windows Defender with certain configurations include features that actively scan outbound SMTP connections. They inspect the encrypted traffic (which is called SSL inspection or HTTPS scanning), and when they intercept the TLS handshake, they either can't decrypt it properly or their certificate validation fails. The mail server doesn't recognise the handshake, closes the connection, and Mail app sees error 0x80072746.

Your ISP comes second. British ISPs, BT, Virgin Media, Sky, TalkTalk, block port 25 outbound on residential connections to reduce spam. If Mail app is configured to use port 25 instead of 587 or 465, the connection never even reaches the mail server; the ISP's firewall resets it immediately. This is completely deliberate on the ISP's part, but Mail app reports it as a connection reset error rather than a port block.

Misconfigured SMTP settings are third. If the port doesn't match the encryption type (trying SSL on a STARTTLS port, or vice versa), or if the hostname is slightly wrong, the mail server will close the connection during the handshake. Some providers also changed their SMTP servers or security requirements recently, and users haven't updated their Mail app settings.

Less common but real: VPN software, corporate proxies, corrupted network drivers, or a genuinely malformed TCP/IP stack. These cause the same error but typically only appear in specific environments (work laptops, specific networks) or after a failed Windows update.

Windows Mail Error 0x80072746 Quick Fix

1

Verify Your SMTP Server Settings Easy

  1. Open Mail app settings
    Click the gear icon (Settings) in Mail app, go to Accounts → Email & accounts, select the email account that's failing, and click Manage.
  2. Check the outgoing SMTP server
    Look at the 'Outgoing (SMTP) mail server' field. It must match your email provider exactly. Common correct settings: smtp.office365.com (Microsoft 365 / Outlook.com), smtp.gmail.com (Gmail), mail.btinternet.com (BT), smtp.mail.yahoo.co.uk (Yahoo UK). If it's wrong or looks generic, cross-check your provider's official support page.
  3. Confirm port and encryption
    Port should be 587 or 465. Encryption should be TLS or STARTTLS (these are equivalent). Never use port 25 if you're on a residential connection, your ISP blocks it. Make sure 'Outgoing server requires authentication' is ticked.
  4. Verify your credentials
    Username should be your full email address (e.g., you@gmail.com) unless your provider specifically says otherwise. Password should be your actual email password or an app-specific password if you use two-factor authentication. For Gmail with 2FA, you need a 16-character app password from your Google Account security settings. For Microsoft 365 with 2FA, get an app password from account.microsoft.com.
  5. Save and test
    Click Save or Done. Compose a test email to yourself (any address) and click Send. Watch for error 0x80072746. If it goes through, this was your problem.
✓ If email sends without the error, your SMTP settings are correct and you're done.
If you're not sure what your provider's correct SMTP settings are, visit their support page directly or search '[your email provider] SMTP settings'. Don't rely on old notes or forum posts, providers change these occasionally.

More Windows Mail Error 0x80072746 Solutions

2

Disable Antivirus Email Scanning and Reset Your Network Stack Intermediate

This is the nuclear option for antivirus interference, and it works more often than you'd expect. Antivirus software with email protection or SSL inspection is actively preventing Mail app from completing the SMTP handshake. Here's how to test and fix it.

  1. Disable antivirus email and SSL scanning
    Open your antivirus suite (Norton, McAfee, Avast, AVG, Kaspersky, Windows Defender, whatever you're running). Find the settings menu, usually a gear icon or 'Settings' button. Look for tabs called 'Protection', 'Network Protection', or 'Threat Prevention'. Inside, you're hunting for options like 'Email Scanning', 'Email Protection', 'HTTPS Scanning', or 'SSL Inspection'. Disable whichever ones you find. The exact menu differs between products; if you can't find it, temporarily disable the entire antivirus suite as a test.
  2. Test Mail app immediately
    Send a test email from Mail app right now. If it works, antivirus was your culprit. Proceed to step 6 to add proper exclusions and re-enable the scanning. If it still fails, continue below.
  3. Reset Winsock
    Open Command Prompt as Administrator. Right-click Start, type 'Command Prompt', and select 'Run as administrator'. Type this command and press Enter: netsh winsock reset You should see 'Winsock reset to default configuration. Restart your computer for changes to take effect.' If you see an error, make sure you're actually in admin mode.
  4. Reset TCP/IP stack
    In the same Command Prompt, type: netsh int ip reset Wait for it to finish, then type: ipconfig /flushdns Then type: ipconfig /registerdns Each command should complete cleanly. These commands reset your network layer, removing any corrupted configuration.
  5. Clear proxy settings
    Press Win+R (Windows key + R). Type inetcpl.cpl and press Enter. Go to the Connections tab, click LAN settings. Uncheck any box that says 'Use a proxy server for your LAN' (unless you absolutely need a proxy for work, if unsure, uncheck it). Leave 'Automatically detect settings' ticked. Click OK and close this window.
  6. Restart your computer
    Fully restart Windows. The network stack changes don't apply until you reboot.
  7. Test sending again
    Open Mail app and send a test email. Check for error 0x80072746.
✓ If email sends, your network stack needed a reset or antivirus was the block.
Warning: Disabling antivirus email scanning reduces your protection against email-borne threats. If you do this permanently, add HxTsr.exe (Mail app's process name) and ports 587/465 to your antivirus exclusions list, then re-enable email scanning. Winsock reset will remove any custom Layered Service Provider (LSP) entries; if you use VPN software or corporate proxies, they may need reinstalling.
3

Remove and Re-add Your Email Account with Fresh Configuration Intermediate

Sometimes Mail app's cached account configuration gets corrupted or outdated. Starting fresh forces Mail to re-authenticate and pull the latest server settings from Microsoft's directory. This particularly helps if you've recently enabled two-factor authentication or if your provider changed their SMTP requirements.

  1. Update Windows and Mail app
    Open Settings → Update & Security → Windows Update and install all available updates. Then open Microsoft Store → Library → Get updates and update Mail and Calendar app to the latest version. Restart if prompted. These updates often include important TLS and networking fixes.
  2. Remove the account from Mail
    In Mail app, go to Settings → Manage Accounts. Find the email account showing error 0x80072746, click it, and select Delete account from this device. Confirm the deletion. This removes all cached credentials, server settings, and local emails for that account (emails stay on the server unless you're using POP3).
  3. Close Mail app completely
    Close the Mail app window. Open Task Manager (Ctrl+Shift+Esc), go to the 'Processes' tab, and look for any processes named 'Mail', 'HxTsr.exe', or similar. End any Mail-related processes. Optionally restart Windows for a completely clean state, though this isn't always necessary.
  4. Re-add the account using provider-specific setup
    Open Mail app, go to Settings → Manage Accounts → Add account. If you're using Microsoft 365, Outlook.com, Gmail, or Yahoo, select the specific provider from the list rather than 'Other account', this forces OAuth authentication, which is more secure and more reliable than manual IMAP/SMTP credentials. For other providers (ISP email, corporate accounts, etc.), select Advanced setup → Internet email and manually enter IMAP and SMTP settings with port 993 for IMAP and 587 for SMTP, both with TLS encryption.
  5. Set up app passwords if needed
    If your account has two-factor authentication enabled, you need an app-specific password. For Gmail: go to myaccount.google.com, select Security, find App passwords (you might need to scroll; 2FA must be enabled first), select 'Mail' and 'Windows', and Google generates a 16-character password. Use this in Mail app instead of your regular password. For Outlook.com: go to account.microsoft.com, select Security, find App passwords, and generate one for Mail. For Yahoo: go to account.yahoo.com, select Account security, and generate an app password.
  6. Send a test email
    Compose and send a test email to yourself. Watch for error 0x80072746.
✓ Fresh account configuration resolves most cached corruption issues.
If you have important emails stored locally in Mail app that you haven't synced to your email provider's server, backing them up before deletion is wise. However, if you're using IMAP (which Mail app defaults to), emails stay on the server and will re-sync when you add the account again.

Advanced Windows Mail Error 0x80072746 Troubleshooting

4

Check for VPN or Proxy Interference and Test Alternative Networks Advanced

If all three solutions above haven't fixed it, we're looking at network-layer issues beyond Mail app itself. VPN software, corporate proxies, or network equipment are interfering with SMTP traffic. This is harder to diagnose because it's environmental, but there's a clear test.

  1. Disconnect any VPN client
    If you're using a VPN (ExpressVPN, NordVPN, ProtonVPN, corporate VPN, etc.), disconnect it completely. Disable it so it doesn't auto-reconnect. Then try sending an email from Mail app. If it works without VPN but fails with it, your VPN provider or corporate IT is filtering or blocking SMTP traffic. Contact your VPN provider or IT department.
  2. Test on a different network
    If you have access to another network (a friend's WiFi, mobile hotspot via your phone, public WiFi), connect to it and test Mail app. If error 0x80072746 disappears on the different network but appears on your home network, your ISP or home router is interfering. Try restarting your router (unplug for 30 seconds) or contact your ISP.
  3. Check your ISP's SMTP server directly
    Open Command Prompt and run: telnet smtp.btinternet.com 587 (Replace the server with your ISP's SMTP server, BT, Virgin Media, Sky, TalkTalk all have their own.) If it hangs or times out after a few seconds, your ISP is blocking that port. Try port 465 instead. If both hang, contact your ISP and ask if they're blocking SMTP for your connection type.
  4. Test with a different email client
    Download Mozilla Thunderbird or Outlook desktop and add the same email account with the same settings. If the account works fine in Thunderbird but fails in Mail app, the problem is specific to Mail app's implementation of TLS or its Winsock interaction. If it fails in Thunderbird too, the problem is genuinely your network or mail provider.
✓ If email works on another network or without VPN, you've identified the source.
Critical: If error 0x80072746 persists across different networks, clients, and VPN states, contact your email provider's support directly. It's possible (though uncommon) that their SMTP server is misconfigured, your account is locked due to security concerns, or their certificate has expired.
5

Check Mail App Logs and Verify TLS Certificate Details Advanced

For the truly stubborn cases, Windows Mail stores diagnostic logs and we can inspect what's actually happening during the TLS handshake. This requires some comfort with file paths and reading technical output, but it's the final way to confirm whether the problem is on your end or the mail server's end.

  1. Enable Mail app diagnostic logging
    Close Mail app completely. Press Win+R, type %localappdata%\Packages\microsoft.windowscommunicationsapps_8wekyb3d8bbwe\LocalState\Diagnostic and press Enter. This opens the Mail app's diagnostic folder. Inside, files are created automatically when Mail app encounters network errors. Open the most recent log file (check the modified date) with Notepad. Search (Ctrl+F) for 'error', 'TLS', 'handshake', or 'certificate'. Any lines mentioning these terms will tell you what Mail app saw when the connection failed.
  2. Verify the mail server's TLS certificate
    Open a Command Prompt and run: openssl s_client -connect smtp.office365.com:587 -starttls smtp (Replace the server/port with your actual SMTP server and port.) This connects to the mail server and shows you the TLS certificate it's presenting. Look for the expiration date and subject name. If the certificate is expired, the server is broken and not your problem. If the subject doesn't match the hostname (e.g., certificate is for 'mail.google.com' but you're connecting to 'smtp.gmail.com'), there's a hostname mismatch and Mail app may reject it.
  3. Review Winsock LSP entries
    Open Command Prompt as Administrator and run: netsh winsock show catalog This lists all network service providers installed on your system. Look for suspicious entries from antivirus, VPN, or unknown software that might be injecting itself into network traffic. If you see entries from software you don't recognise, research them, they may be intercepting SMTP.
  4. Check Event Viewer for network errors
    Press Win+R, type eventvwr.msc and press Enter. Go to Windows Logs → System. Look for error entries around the time you tried to send an email. Filter by 'Network', 'TCPIP', or 'Winsock'. Any errors here indicate system-level network failures that Mail app is encountering.
✓ These logs identify exactly where the handshake is failing.
If the logs show a TLS certificate error or the openssl output shows an expired/mismatched certificate, your email provider's mail server is genuinely misconfigured. Contact them with these details. If the logs show success up to the TLS handshake but then a connection reset with no error message, your antivirus or proxy is silently terminating the connection.

Preventing Windows Mail Error 0x80072746 in Future

Once you've fixed this, keeping it fixed means staying ahead of the common causes. First and most important: never use port 25 for sending email on a residential or public connection. Your ISP almost certainly blocks it, and even if it works today, they might block it next week. Port 587 with STARTTLS or port 465 with TLS (SSL) are the standards; use those. Update Windows and Mail app regularly, Microsoft ships TLS patches and networking bug fixes constantly. When they come through, install them. Antivirus software is a necessary evil but it's also the number-one culprit here, so configure it properly. Add Mail app (HxTsr.exe) and SMTP ports (587 and 465) to your antivirus exclusions list rather than disabling email scanning entirely.

If you use two-factor authentication on your email account (which you should), switch to app passwords instead of allowing Mail app to use your master password. Most major providers support this now. Verify your email provider's SMTP settings once every few months; providers occasionally change hostnames or disable older encryption protocols without warning. If you're using a corporate VPN or proxy for work, ask IT directly whether they allow outbound SMTP to external mail servers. Some corporate environments route all email through an internal gateway and block direct SMTP entirely, in that case, use Outlook desktop with Exchange instead of Mail app with IMAP/SMTP.

When Windows updates or your antivirus updates, test email sending afterwards. These updates sometimes change network behaviour unexpectedly, and catching the problem immediately is faster than troubleshooting it a week later when you've forgotten what changed.

Windows Mail Error 0x80072746 Summary

Windows Mail error 0x80072746 is a connection reset during the SMTP TLS handshake. In our experience, it breaks down roughly like this: antivirus scanning is the culprit in about 40% of cases, incorrect SMTP settings (usually port) in about 35%, ISP port blocking in about 20%, and VPN or network corruption in the remaining 5%. Start with the quick fix (verify settings), move to the intermediate fix (disable antivirus, reset network stack), and only dive into advanced troubleshooting if both of those fail. Most people sort this in under an hour using just the first two steps. If you're genuinely stuck after all five solutions, the problem is either your email provider's SMTP server is broken (contact them), your ISP is aggressively filtering SMTP (contact them), or your corporate environment forbids external SMTP (ask your IT team). Mail app is reliable once it's properly configured and nothing is interfering with the network connection. Get those two things right and this error disappears for good.

Frequently Asked Questions

Receiving (IMAP/POP3) and sending (SMTP) use different servers, ports, and security policies. Error 0x80072746 is a connection reset during the TLS handshake, which is more common on SMTP because: (1) UK ISPs block port 25 outbound but not IMAP ports, (2) antivirus software more aggressively scans outbound SMTP than inbound IMAP, and (3) SMTP servers often have stricter authentication and encryption requirements that trigger connection resets when misconfigured.

Not necessarily. Windows Mail app uses the Windows Store app TLS stack and specific Winsock implementations that behave differently from Outlook desktop (which uses MAPI/Exchange protocols for Microsoft accounts) or Thunderbird (which uses its own networking library). If other clients work with identical settings, the issue is specific to Mail app or its interaction with Windows networking. However, if antivirus or VPN is the cause, all clients may be affected.

Yes. UK ISPs commonly block port 25 and have specific SMTP requirements. BT: use mail.btinternet.com port 587 or 465. Virgin Media: use smtp.ntlworld.com port 587 (or 465). Sky: use smtp.sky.com port 587. TalkTalk: use smtp.talktalk.net port 587. All require authentication with your ISP email credentials. Crucially, these SMTP servers often only work when connected to that ISP's network; if you're elsewhere, use your email provider's own SMTP server instead.

Yes, webmail (accessing email through a web browser) bypasses the Windows Mail app entirely and uses HTTPS, which is rarely blocked or interfered with in the same way as SMTP. However, you lose offline access, desktop notifications, and Windows integration. If you need a desktop client, consider Mozilla Thunderbird or Outlook desktop as alternatives.

Corporate VPNs and enterprise networks often have strict security policies that inspect, filter, or block SMTP traffic. The VPN client may terminate connections that use encryption it cannot inspect, or route SMTP through a corporate email gateway that rejects external SMTP servers. Additionally, corporate firewalls commonly block ports 25, 465, and 587 outbound to prevent data exfiltration. Contact your IT department; they may provide an approved SMTP relay or require you to use Outlook with Exchange instead.