How to Troubleshoot 421 4.4.2 Connection Dropped Error

Cybersecurity

Fix the 421 4.4.2 connection dropped due to connection reset error in Outlook or Gmail. Learn causes, related SMTP issues, and troubleshooting steps.

by Milena Baghdasaryan

Reading Time: 5 min
How to Troubleshoot 421 4.4.2 Connection Dropped Error
Table Of Contents−

Key Takeaways

  1. The 421 4.4.2 Connection Dropped error signals an issue on the recipient’s server or a network problem.
  2. Sender-side complications and TLS handshake failures/timeouts may also be the cause of the 421 4.4.2 Connection Dropped error.
  3. You can diagnose the error by checking SMTP logs, sending limits, and mail server.
  4. The error can be resolved by reviewing security and firewall settings, verifying authentication credentials, etc. Sometimes, it may resolve automatically.
  5. In some cases, you might need to escalate the issue to Gmail or Microsoft support.

Fix the “421 4.4.2 Connection Dropped” error by identifying DNS misconfigurations, firewall restrictions, or network failures that block SMTP server connections. Restoring mail flow requires targeted checks of server settings, DNS resolution, and external connectivity.

What Does the SMTP Error “421 4.4.2” Mean?

421 4.4.2 Connection Dropped error indicates a temporary issue on the recipient’s server. It may also signal a network problem that prevents a stable connection. While the issue sometimes resolves on its own, that’s not always the case. Sometimes, more proactive troubleshooting is necessary.

Approximately 16.9% of all emails fail to reach their intended recipients due to delivery errors, and the 421 4.4.2 error is a significant contributor. For marketing professionals, this can be a nightmare, as failed deliveries can derail carefully planned campaigns and waste valuable effort.

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Common Causes of 421 4.4.2 Errors and Connection Resets

Here are some factors that may lead to 421 4.4.2 Connection Dropped SMTP error. 

Recipient Server Problems

If the recipient’s mail server is temporarily offline or overloaded, then the connection error is expected. 

TLS Handshake Failures or Timeouts

Sometimes, a secure communication (TLS) is required, but the handshake between your server and the recipient’s server fails or times out. In this case, the connection will drop. 

Network Issues

Network congestion, slow internet speeds, or strict firewall rules can also cause connection timeouts. Some Internet Service Providers impose sending limits, and when you exceed these, the 421 4.4.2 error will be triggered. 

Sender-Side Complications

Incorrect SMTP authentication credentials, sending an excessive number of emails too quickly (leading to rate throttling by the recipient’s server), or misconfigured email relay settings (e.g., incorrect smart host settings) can also trigger  421 4.4.2 Connection Dropped error. 

How to Diagnose the 421 4.4.2 Error?

Here are some steps you can take to pinpoint the cause of a 421 4.4.2 Connection Dropped error.

Check SMTP Logs

Review your email server’s SMTP logs to find specific socket errors or connection failure messages.

Utilize Network Tools

You can make use of the following network tools:

  • Wireshark for packet capture
  • netstat for network connection status
  • openssl s_client for diagnosing TLS handshake issues

Check Sending Limits

Make sure you haven’t exceeded any submission rates or sending limits. These may be imposed by your email provider or the recipient’s server. In any case, you should always abide by the limit. 

Ensure a ‘Happy’ and Healthy Mail Server 

Ensure your mail server is healthy and operating correctly. It would be ideal if you could also check the recipient’s mail server. 

How to Troubleshoot SMTP Error 421 4.4.2

Once you are done with your diagnosis, it’s now time to resolve the 421 4.4.2 error:

Step 1: Check the Recipient’s Email Server Status

Use online tools to test the recipient’s domain’s DNS records, MX entries, or SMTP responsiveness. If issues persist, consider contacting the recipient’s IT team directly to inquire about outages on their end.

Step 2: Verify DNS Records are Correctly Configured

Ensure your domain’s A, MX, and PTR records are set up accurately. Also, confirm the MX records for the recipient’s domain are valid.

Step 3: Review Security and Firewall Settings

Check that your firewall rules aren’t inadvertently blocking outgoing SMTP connections. If you’re using a cloud-based email service, ensure your sending IP address is whitelisted. Temporarily disabling antivirus software can help determine if it’s interfering with email delivery.

Step 4: Ensure Robust Network Connectivity

Run a ping test to the recipient’s mail server (if known) or a reliable public DNS server like 8.8.8.8 to check for latency. For a more detailed path analysis, use tracert on Windows or traceroute on Linux. If you detect high latency or packet loss, contact your Internet Service Provider.

Fixes and Workarounds: Optimizing SMTP Configurations

Here are some helpful actions for optimizing your SMTP configuration. 

Choose the Right Port

Port 25 is the default for SMTP. However, many ISPs block it. Port 587 (with STARTTLS) is the recommended standard for secure email submission. Port 465,  on the other hand, is a deprecated standard even though it does support SMTP over SSL/TLS.

Verify Authentication Credentials

Double-check (or even triple-check) that your SMTP authentication credentials are accurate and up-to-date. This includes both usernames and passwords.

Adjust Sending Limits

Don’t ever send bulk emails in a single batch. Instead, distribute your sending over time. This will prevent you from surpassing the sending limit (which in turn could lead to rate throttling). If you don’t know what your provider’s limits are, contact them to find out.

When to Escalate

Sometimes, the issues persist regardless of all the above-mentioned actions. In such cases, you should escalate them. 

For Microsoft 365 (Outlook)

Visit https://admin.cloud.microsoft. Then, select “Help & support” in the bottom right. Describe your problem: provide detailed error logs, timestamps, etc.

For Gmail (Google Workspace Users)

Google Workspace administrators have access to support channels. But for individual Gmail users, there is often no direct support for generic SMTP errors. Instead, you can make use of help articles and community forums.

Best Practices for Email Deliverability

Email authentication protocols like SPF, DKIM, and DMARC are not direct fixes for 421 4.4.2 errors. However, they can help improve your email deliverability, reputation, and reduce the chances of them being flagged as spam. This contributes to a more authentic and reliable email communication. 

Summing Up

421 4.4.2 Connection Dropped error may resolve with time. But it might also not. To troubleshoot, get it diagnosed with network tools, server logs, and correct SMTP configurations. If you can’t resolve the problem by yourself, try to get direct help from Microsoft or Gmail support. 

PowerDMARC helps you monitor email threats and fix email deliverability issues that occur as a result of missing or invalid authentication setups. Get in touch today to get inbox-ready in no time! 

Frequently Asked Questions (FAQs)

Does the 421 4.4.2 Connection Dropped indicate a problem? 

The 421 4.4.2 Connection Dropped error implies your email server couldn’t maintain a stable connection with the recipient’s mail server. 

Can DMARC prevent the 421 4.4.2 Connection Dropped error?

No. But DMARC can boost email deliverability and reduce spam.

How can I get rid of the 421 4.4.2 connection issue?

Check your email server, DNS MX records, and network connectivity.

Is 421 4.4.2 a security risk?

Usually, the 421 4.4.2 Connection Dropped is not a security risk. But hackers may be able to exploit an unstable connection.

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