SMTP Error 421 4.4.1 – No Answer From Host: How to Fix It

What causes SMTP Email Error 421 4.4.1?

It is a specific form of the SMTP Email Error 421. It happens when the server that sent the email tries to connect with the email server of the receiver but does not get a response. The reasons can be any of the following:

Network connectivity issues

Emails need stable networks and temporary problems of weak networks may lead to SMTP Email Error 421 4.4.1. The connection could be blocked for security policies, wrong firewall settings, etc. Moreover, when the sender’s server suffers from DNS resolution failures (when a DNS server fails to resolve a domain name to the associated IP address), it will also fail to connect.

Recipient mail server issues

If the receiving mail server is down, then the sending mail server fails to create a connection. The recipient’s email server could be down for maintenance or an outage. If it has a high number of concurrent requests, the receiving mail server may not be able to respond as well.

Sender-side problems

If the sender’s IP is on spam blacklists, the recipient’s server could reject the connection. Also email providers may “throttle” your email delivery, which means they have sending limits to prevent spam. This throttling strategy temporarily rejects connections.

How to troubleshoot and fix SMTP Email Error 421 4.4.1

Resolving the SMTP 421 4.4.1 error requires a structured approach to diagnosing and fixing the underlying causes. Below are some of the most effective troubleshooting steps you can do on your end. Even if it is a temporary issue, the delay it has caused may affect businesses in the long run. 

For Gmail users

• Check if you can connect to the Internet. Make sure you’re able to access the Internet and that the connection is stable. You can test this by trying to access other websites or services.
• Verify SMTP server settings. Double-check your Gmail SMTP settings are correctly configured. SMTP server should be smtp.gmail.com, using SSL (or TLS) on port 465 (or 587).
• Verify if your SMTP server can reach other external domains. Try sending a test email to a different email account outside the domain experiencing the issues. (ex. Free email provider, such as Gmail.)
• Contact Gmail support. For the most direct route, try visiting the Gmail Help Center at support.google.com/mail.

For Yahoo! users

• Conduct SMTP compatibility review. Make sure your account settings align with Yahoo’s SMTP requirements: smtp.mail.yahoo.com as the server, SSL required, port 465.
• Review security settings. Adjust security settings or app passwords, to ensure they don’t block SMTP connections.
• Adhere to Yahoo’s requirements for email senders. These guidelines include maintaining your spam rate below 0.3%, authenticating your email by implementing SPF, DKIM, and DMARC, and ensuring a valid forward and reverse DNS record for sending IPs.

For Outlook users

• Reset your email account configuration. In new accounts, SMTP 421 errors occur due to simple misconfiguration of an account’s SMTP settings. Simply head over to Account Settings, removing the email account, and adding it back again.
• Configure your SMTP settings correctly. Make sure they are accurate. The server address usually follows the format smtp.office365.com with SSL encryption on port 587.
• Clear your outbox and retry. Stuck emails can cause these errors sometimes. Try clearing your outbox before attempting to send an email again.
• Update your software. Keeping Outlook updated can resolve many issues, including SMTP errors.

How to prevent this error in the future

Receiving the SMTP 421 4.4.1 error can be annoying, particularly if it interrupts important email communication. The good news is there are some proactive steps you can take to prevent dealing with this issue again. 

By applying proper email server management procedures, tracking tools and authentication methods, future email transactions can be guaranteed. 

Optimize email server settings

To prevent SMTP errors, it is important to have a well configured email server. This stops it from becoming overloaded, enhancing the server’s reliability through peak periods. Ensure that your email server can handle high volumes of outgoing messages:

• Configure retry intervals in your Mail Transfer Agent (MTA) to automatically reattempt failed deliveries. 
• You may also use some load balancing techniques to share traffic between multiple mail servers. 

Regularly check DNS and MX records

Verify your domain’s DNS settings are set up properly. Here’s what you should do: 

• Periodically check MX records to ensure they are pointing to the correct mail servers.
• Both DNS and MX records are vital to email routing so any misconfigured records would lead to email failure and delivery problems.

Strengthen email security measures

SMTP errors can also be prevented by putting a premium on email security, which is also another way to ensure email delivery. This helps protect emails from being bounced or marked as spam. 

• Enable TLS encryption to encrypt email transmissions. 
• Keep SPF, DKIM, and DMARC records fresh to avoid spoofing and obtain maximum deliverability. 
• You can also implement IP whitelisting to limit your connections to those you trust.

Here’s how Warmy.io can help prevent this error from happening again

While SMTP errors are inevitable due to a number of factors, proactive measures can drastically reduce their occurrence and impact. Warmy.io offers a range of solutions to enhance email deliverability and prevent SMTP-related issues.

Reliable email warmup

Warmy.io gradually increases email volume through its email warmup service, helping establish credibility with email providers. This prevents emails from being flagged as spam or rejected due to excessive sending, thereby reducing the risk of SMTP 421 4.4.1 errors.

This process mimics natural email activity, allowing email service providers to recognize the sender as legitimate and trustworthy. Slowly increasing the number of emails sent each day prevents sudden spikes that can trigger spam filters or SMTP errors.

Additionally, Warmy operates with an engagement-driven approach by ensuring emails receive positive engagement (opens, replies, and clicks), reinforcing the sender’s credibility even more. Whether you’re using Google Workspace, Microsoft 365, or custom SMTP configurations, Warmy.io adapts to your platform to optimize deliverability.

Email deliverability test

Warmy.io offers free email deliverability tests to check the likelihood that your emails will land in inboxes instead of spam folders.

This allows you to proactively address potential deliverability problems before they impact your campaigns.

The inbox placement analysis lets you see the percentages of emails landing across different providers (Gmail, Outlook, Yahoo, etc.). Regular scans also ensure that your sending IP and domain remain free from spam blacklists that could cause SMTP 421 errors.

And if somehow, your domain gets blacklisted, you’ll find out right away so you can proceed with the delisting process.