Struggling with email deliverability? Have your marketing emails been blocked, or do you keep encountering cryptic SMTP error codes? 

If you’ve ever seen an SMTP error message with just a few confusing words, you’re not alone. 

These codes are part of a standardized system used by email servers to communicate the status of your email—whether it’s successfully delivered or why it failed to reach its destination.

In this guide, we’ll decode the most common SMTP error codes, explain what they mean, and show you how to fix them so your emails get through every time. By the end of this article, you’ll have the knowledge to troubleshoot and resolve SMTP errors quickly and efficiently.

What is an SMTP Error Message?

SMTP, or Simple Mail Transfer Protocol, is the standard protocol that enables email servers to exchange messages with one another. In simpler terms, it's the mechanism that allows emails to travel from the sender to the recipient. Whether you're sending an email from a mobile device, laptop, or desktop, an SMTP server is responsible for delivering your message to the correct destination.

Think of SMTP as a digital postal service, ensuring that your email reaches the right inbox, just like a postal service ensures your letter arrives at the correct address.

When an email is successfully received by the destination server, it sends an SMTP error code back to the sender. These codes are part of the acknowledgment process, informing the sender that the message has been successfully delivered or explaining why it hasn’t. It’s important to note that not all SMTP error codes indicate delivery failure; some simply inform the sender of the server’s status.

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What are Gmail SMTP Settings?

When you first time set up an email account as a Gmail account, the system asks you for SMTP configuration details, so you need to provide and use the settings as mentioned below:

• Gmail SMTP server IP address: smtp.gmail.com
• Gmail SMTP username: Your Gmail address (for example, example@gmail.com)
• Gmail SMTP password: Your Gmail password
• Gmail SMTP port (SSL): 465
• Gmail SMTP port(TLS): 587
• Gmail SMTP TLS/SSL required: Yes

It is important to enter your full Gmail email address as the username for authentication when configuring Gmail's SMTP server. Always use your complete gmail email address to avoid login issues. Make sure to review your gmail settings to ensure SMTP is enabled and properly configured.

If you are using a free gmail account, be aware of sending limits and possible verification warnings, as free accounts have lower limits compared to a Google Workspace account. For higher sending limits and additional features, consider using a Google Workspace account.

When entering your smtp details, such as server address, port, and authentication method, double-check for accuracy to ensure successful email delivery. Incorrect smtp details can cause connection errors.

To set up OAuth authentication, you need to create oauth credentials in the Google Cloud Console by configuring an oauth client and obtaining the oauth client id. Enter the oauth client id in the appropriate client id field during setup. As you proceed, follow the prompts to the next page and carefully review the following screen to complete the multi-step OAuth configuration.

After successful configuration, you should see a success message confirming that your setup is complete.

If you are using WordPress, access the plugin's settings and mailer settings to connect to Gmail's SMTP server. Adjust these settings as needed for your site's emails to be sent reliably through Gmail or Google Workspace.

For personal use, note that certain limitations may apply, while Google Workspace account holders benefit from higher limits and custom domain support. If you are developing a google app for email functionality, ensure it is published and manage permissions in your google accounts accordingly.

If you need to use older authentication methods, you may have to enable less secure apps in your Google Account settings, but it is strongly recommended to use secure apps and OAuth for better security.

To improve email deliverability and authentication, add an spf record and other relevant dns records to your domain's DNS settings.

Gmail's SMTP server can also be used with email clients like microsoft outlook, but proper configuration is required for successful integration.

Using Gmail or Google Workspace to send your site's emails helps ensure reliable delivery and improved security.

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Gmail API and Google Workspace: Advanced Email Sending Solutions

For businesses and developers who need advanced control over their email communications, Gmail API and Google Workspace provide powerful alternatives to standard SMTP. By leveraging the Gmail API, you can automate email workflows, send messages programmatically, and integrate email features directly into your applications or websites. This is particularly beneficial for organizations using Google Workspace, as it offers a customized and professional email experience across all accounts.

Getting Started with Gmail API: A Step-by-Step Guide

To unlock the full potential of Gmail’s advanced email features, follow these steps to set up the Gmail API:

1. Create a Project in Google Cloud Console: Log in to the Google Cloud Console and create a new project for your application or website.
2. Enable Gmail API: Navigate to the Gmail API overview page from the Google Cloud Console sidebar and enable the API for your project.
3. Generate API Credentials: Use the “Create Credentials” button to generate a client ID and client secret. These are essential for authenticating your app’s requests to Gmail.
4. Configure OAuth Consent Screen: Set up the OAuth consent screen, including your app logo and basic information, to provide a secure authentication experience for users.
5. Set Authorized Redirect URIs: In the Google Cloud Console, specify the redirect URIs that will allow your web app or site (like WordPress) to securely complete the authentication process.

Once set up, the Gmail API empowers you to:

• Send emails
• Read messages
• Manage email labels
• And more—all with top-tier security and flexibility.

Integrating Gmail API on WordPress site

For WordPress users, the WP Mail SMTP plugin simplifies the process of connecting your WordPress site to the Gmail API. By configuring the plugin with your client ID and client secret, you can send emails from your WordPress site via Gmail or Google Workspace, significantly improving email deliverability and reducing the chances of emails being flagged as spam.

Why Use Gmail API and Google Workspace?

Whether you’re handling user support emails, automating notifications, or sending password resets, integrating the Gmail API with Google Workspace ensures your site sends emails reliably and securely. This is especially beneficial for businesses that need:

• Higher sending limits
• Advanced email features
• Seamless integration with other Google services (like Google Drive or Google Calendar).

Using Gmail’s advanced API features and Google Workspace gives your organization the flexibility, security, and power to handle email tasks with ease.

How to Read Common SMTP Error Codes?

Not all SMTP error codes indicate a failure. In fact, many of these codes are simply status updates or signals for next steps. Here’s a breakdown of the most common SMTP error codes, along with what they mean and how to address them.

How do I Reset my SMTP Server?

There could be several reasons behind resetting the SMTP client, such as the following:

• Suppose you encounter the "System Error" Failure Sending mail" error message. This error comes when linking bulky attachments with your emails or messages.
• If you encounter the "License information could not be updated" error message. This error comes when you try to update the permission keys' details.
• If you encounter "Error 5.7.1,". This error message comes when the destination email server does not receive the mail or message.
• If you see that the portal notifications are neither being sent to receive.

The above symptoms could occur if the SMTP client stops running, works correctly, or needs a reboot.

What is the Resolution?

When resolving this issue, you need to restart the SMTP service with the below steps:

• Open Windows services
• Scroll down till you see the "Simple Mail Transfer Protocol" icon
• Right-click on it and click "restart."

How do I Enable SMTP in Gmail?

If you are looking to set up SMTP service in your Gmail inbox, you need to follow the below configuration settings for SMTP:

• Open and login into your Gmail account
• Go to "Settings"
• Select the "Forwarding and POP/IMAP" setting from there
• Click on the "IMAP Access" section, and under that, toggle on the option to "Enable IMAP."

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• Now, click on the emails received at the top of your accredible dashboard.
• Click on “SMTP overrides” from the sidebar menu on the left side.
• Enter your Gmail account correct email address and password here. 

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• Further, the details need to be mandatorily filled in as below:‍
• Outgoing Server - smtp.gmail.com‍
• Port - 587‍
• Encryption - TLS‍
• Authentication - Base64 encoded

Now, click on “Save changes.” You can also test the same by sending a testing email from your custom email address.

How do I Fix the SMTP Error on Email?

There could be various reasons why you would be facing email delivery issues while sending emails through the SMTP server, such as

• Internet issues
• Default Post 25 problems, and much more.

So the simple steps to fix or rectify this error message on email are:

• Login into your Gmail account
• Open the “settings” of your email account
• Look for “outgoing SMTP server” and click on its “settings.”
• Check the mentioned current outgoing port, and change it to 587 or 26.
• Ensure to re-enter your Gmail correct email address or username and password again here.
• Click on “Save changes” and then test again.

Best Practices for Configuring Gmail SMTP Server

Setting up your Gmail SMTP server correctly is essential for ensuring your emails are delivered securely and reliably. Follow these best practices to optimize your SMTP settings and avoid common issues.

1. Use a Secure Connection

• Always use SSL or TLS encryption to secure your email communications.
  • SSL: Use port 465.
  • TLS: Use port 587.

Using encryption ensures that your emails are protected during transmission, reducing the risk of interception.

2. Enter the Correct Server Address

• Set the Gmail SMTP server address to smtp.gmail.com in your email client or application.

This ensures that your email client can connect to Gmail's SMTP server to send your emails reliably.

3. Authenticate Properly

• Use your full Gmail address as the username for authentication.
• If two-factor authentication (2FA) is enabled on your Google account, generate an app password and use it instead of your regular Gmail password.

This ensures that your account remains secure while allowing you to send emails without issues.

4. Choose the Right Authentication Method

• Consider using OAuth authentication. Many modern email clients and plugins support OAuth, which is more secure than using plain text passwords.
• If available, enter your client ID and client secret to authenticate your app securely.

OAuth helps protect your Gmail account and prevents unauthorized access.

5. Monitor Gmail’s Sending Limits

• Free Google accounts have daily sending limits. Exceeding these limits can result in temporary blocks or error.
• Google Workspace users benefit from higher sending limits, but it’s still important to monitor usage.

If you're sending large volumes of emails, you may encounter rate limits that prevent further delivery.

6. Test and Monitor Regularly

• After configuring your SMTP settings, send a test email to confirm everything is working.
• Regularly monitor your email client or plugin settings for any error messages or issues.

By testing regularly, you can ensure that your SMTP configuration is always running smoothly.

7. Leverage WP Mail SMTP Plugin for WordPress

• For WordPress websites, the WP Mail SMTP plugin simplifies the process of setting up SMTP details, managing authentication, and logging sent emails.
• This plugin also provides helpful troubleshooting tools if you encounter delivery problems.

Using this plugin ensures better integration with Gmail's SMTP and helps you manage email deliverability efficiently.

8. Consider Dedicated Email Services for High Volume

• If your website sends large volumes of emails, consider using a dedicated email delivery service like Mailtrap.
• This helps bypass Gmail’s sending limits, improving email deliverability and ensuring that your messages are not flagged as spam.

For businesses with high email traffic, dedicated services offer better scalability and rel

Optimize Your Email Campaigns for Better Deliverability

This guide has explained what SMTP error codes are and how to troubleshoot common email delivery issues. While these error codes might seem like roadblocks, they often provide important information to help you get your emails back on track quickly.

The main causes of SMTP errors usually stem from incorrect SMTP configurations or network connection problems. By following the steps outlined in this guide, you can resolve most SMTP issues and ensure smoother email communication.

But if you’re looking for a more scalable solution to handle high-volume email campaigns or if you find managing SMTP settings too complex, Smartlead is here to help. With features like SmartServers, inbox rotation, and automatic troubleshooting, Smartlead helps you manage email campaigns without the hassle of constant SMTP errors.

Ready to streamline your email outreach and boost deliverability?
Sign up for Smartlead today and experience seamless, high-quality email delivery with advanced automation tools that handle the heavy lifting for you.

Frequently Asked Questions

Why am I suddenly unable to send emails?

Sudden issues with sending emails can arise from various factors including internet connectivity problems, incorrect SMTP (Simple Mail Transfer Protocol) server settings, or SMTP authentication issues. It's important to check your internet connection, verify your SMTP server settings are correct, and ensure that SMTP authentication is enabled for your email client.

How do I fix email not connecting to the server?

To resolve issues with email not connecting to the server, follow these steps:

1. Check Your Internet Connection: Ensure you have a stable connection.
2. Verify SMTP Server Settings: Double-check the server address, port number, and encryption method are correctly configured.
3. Enable SMTP Authentication: Make sure SMTP authentication is active with the correct credentials.
4. Restart SMTP Service: On your device or computer, restart the SMTP service.
5. Send a Test Email: Test the connection and setup by sending a test email.

Why is my SMTP blocked?

SMTP can be blocked due to incorrect server settings, IP blacklisting, or security restrictions implemented by your email service provider or IT department. To unblock it:

1. Ensure Correct Server Settings: Verify that your SMTP server settings are accurate.
2. Check for IP Blacklisting: Investigate if your IP address has been blacklisted and follow steps to remove it.
3. Inquire About Security Restrictions: Contact your email service provider or IT department regarding any SMTP blocks.
4. Use a Different SMTP Server: Consider switching to an alternative SMTP server or service if necessary.

Do I need SMTP server to receive email?

No, an SMTP server is not required to receive emails. SMTP is primarily used for sending emails. To receive emails, your email client or web-based email service should support POP3 (Post Office Protocol 3) or IMAP (Internet Message Access Protocol) protocols.

How do I know if my SMTP authentication is disabled?

To check if SMTP authentication is disabled, you can:

1. Access Email or Account Settings: Open your email client and go to the SMTP server settings or advanced settings.
2. Look for SMTP Authentication Option: Find the option to enable or disable SMTP authentication.
3. Enable If Disabled: If you find the option disabled, enable it and save your settings.
4. Test With a Test Email: Send a test email to confirm SMTP authentication is functioning correctly.

How do I troubleshoot my SMTP relay?

Troubleshooting your SMTP relay involves several steps:

1. Verify Server Settings: Confirm that your SMTP server settings, including address, port, and authentication details, are correct.
2. Check Internet Connection: Ensure your internet is stable and not interfering with SMTP relay.
3. Review Email Provider Restrictions: Determine if there are any limitations or restrictions on SMTP relaying by your email service provider or network administrator.
4. Conduct a Test Email: Send a test email to verify the SMTP relay is operational.
5. Seek Further Assistance: If problems persist, contact your email service or IT department for additional support.

Understanding the nuances of SMTP and troubleshooting related issues are crucial for maintaining effective email communication. Ensuring correct settings, enabling necessary authentications, and staying informed about service provider restrictions can significantly minimize SMTP-related errors and disruptions in your email activities.