What is SMTP Error? Steps to Decode & Resolve the Error

Created On:
July 19, 2023
Updated On:
November 14, 2023
Resolving SMTP errors

Do you ever wonder why the mail servers are canceling your marketing emailing? And you get some SMTP error code with some small message? It must be clarified because the error code needs to give an easy-to-understand definition or message. 

So let us move ahead in this article and learn a lot more about the SMTP error codes along with all the details of the error codes. 

What is an SMTP Error Message in the Mail?

SMTP stands for Simple Mail Transfer Protocol. Simply put, this is the mechanism used between the mail servers for exchanging emails. 

Any email sent from a mobile device or a laptop uses an SMTP server to allow that email to be delivered to the destination email server. Or you can also think about SMTP as your postal service that ensures your emails or messages reach the right person and location. 

Whenever a mail is received appropriately at the destination, the destination email server will generate and send an SMTP error code back to the email sender as a confirmation message of acknowledgment. This shows that all SMTP error codes are not technical or delivery failure codes.

smtp server error settings

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

error and smtp settings

Accurate Meaning of the Common SMTP Error Codes

We all know that all the SMTP error codes are not wrong or failed. So let us go through the below and understand this error codes better.

SMTP 101: The sender server unable to connect to the mail server.

SMTP 111: The SMTP connection to the server is refused.

SMTP 211: Generic system status message.

SMTP 220: SMTP service is ready.

SMTP 221: SMTP service has a closing connection.

SMTP 250: The mail or message was delivered to the destination email server without errors.

SMTP 252: The server cannot verify the recipient but will deliver the mail or message.

SMTP 354: The recipient mail server is ready to take the mail or message from the email sender.

SMTP 421: The SMTP service is unavailable, and the connection to server failed. 

SMTP 441: The recipient's mail server is not responding.

SMTP 449: This is a routing error message.

SMTP 450: The given SMTP sequence of commands failed.

SMTP 451: The given SMTP command aborted because of a recipient server error.

SMTP 500: Server unable to recognize the command due to syntax errors.

SMTP 501: There is a syntax error in the command arguments.

SMTP 502: The given command is not implemented.

SMTP 503: The server encountered a wrong sequence of commands.

SMTP 510: Recipient email address is a bad email address.

SMTP 441: The recipient's email address denied receiving your mail or message.

SMTP 550: The given or requested command failed because the recipient mailbox was service unavailable.

SMTP 551: The recipient server is not locally connected.

SMTP 554: The transaction failed.

SMTP 552: The recipient mailbox needs more space to receive your mail or message.

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."

configuring error in smtp settings
  • 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. 
troubleshooting smtp error
  • 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.


The above guide explains what SMTP error codes are and how to resolve them. SMTP error codes are like informational errors so that they can be easily and quickly rectified. The main reason behind them is switching the internet network connection port on your laptops or mobile devices. 

What’s a Rich Text element?

The rich text element allows you to create and format headings, paragraphs, blockquotes, images, and video all in one place instead of having to add and format them individually. Just double-click and easily create content.

  • dfbvrsg
  • svsv

Static and dynamic content editing

A rich text element can be used with static or dynamic content. For static content, just drop it into any page and begin editing. For dynamic content, add a rich text field to any collection and then connect a rich text element to that field in the settings panel. Voila!

How to customize formatting for each rich text

Headings, paragraphs, blockquotes, figures, images, and figure captions can all be styled after a class is added to the rich text element using the "When inside of" nested selector system.

Author’s Details

Tanmay Shukla

Tanmay is a SEO Content Writer at Smartlead. His zeal and enthusiasm in writing led him to the path of being a Content Writer. He has been advancing in this field by possessing more knowledge and skills. His constant endeavor has made him a whiz in SEO, Creative Writing, and driving sales through writing.


Edited by:

Charu Mitra Dubey


People will also read

Frequently asked questions

General Questions

What is Smartlead's cold email outreach software?

Email automation FAQs- Smartlead

Smartlead's cold email outreach tool helps businesses scale their outreach efforts seamlessly. With unlimited mailboxes, fully automated email warmup functionality, a multi-channel infrastructure, and a user-friendly unibox, it empowers users to manage their entire revenue cycle in one place. Whether you're looking to streamline cold email campaigns with automated email warmups, personalization fields, automated mailbox rotation, easy integrations, and spintax, improve productivity, or enhance scalability with subsequences based on lead’s intentions, automated replies, and full white-label experience, our cold email tool implifies it in a single solution.

How does the "unlimited mailboxes" feature benefit me?

Email automation FAQs- Smartlead

Our "unlimited mailboxes" feature allows you to expand your email communications without restrictions imposed by a mailbox limit. This means you won't be constrained by artificial caps on the number of mailboxes you can connect and use. This feature makes Smartlead the best cold email software and empowers you to reach a wider audience, engage with more potential customers, and manage diverse email campaigns effectively.

What do you mean by "unibox to handle your entire revenue cycle"?

Email automation FAQs- Smartlead

The "unibox" is one of the unique features of Smartlead cold email outreach tool, and it's a game-changer when it comes to managing your revenue cycle. The master inbox or the unibox consolidates all your outreach channels, responses, sales follow-ups, and conversions into one centralized, user-friendly mailbox.

With the "unibox," you gain the ability to:
1. Focus on closing deals: You can now say goodbye to the hassle of logging into multiple mailboxes to search for replies. The "unibox" streamlines your sales communication, allowing you to focus on what matters most—closing deals.

2. Centralized lead management: All your leads are managed from one central location, simplifying lead tracking and response management. This ensures you take advantage of every opportunity and efficiently engage with your prospects.

3. Maintain context: The "unibox" provides a 360-degree view of all your customer messages, allowing you to maintain context and deliver more personalized and effective responses.

How does Smartlead ensure my emails don't land in the spam folder?

Email automation FAQs- Smartlead

Smartlead, the best cold email marketing tool, ensures your emails reach the intended recipients' primary inbox rather than the spam folder. 

Here's how it works:
1. Our "unlimited warmups" feature is designed to build and maintain a healthy sending reputation for your cold email outreach. Instead of sending a large volume of emails all at once, which can trigger spam filters, we gradually ramp up your sending volume. This gradual approach, combined with positive email interactions, helps boost your email deliverability rates.

2. We deploy high-deliverability IP servers specific to each campaign. 

3. The ‘Warmup’ feature replicates humanized email sending patterns, spintax, and smart replies.
4. By establishing a positive sender reputation and gradually increasing the number of sent emails, Smartlead minimizes the risk of your emails being flagged as spam. This way, you can be confident that your messages will consistently land in the primary inbox, increasing the likelihood of engagement and successful communication with your recipients.

Can I integrate Smartlead with other tools I'm using?

Email automation FAQs- Smartlead

Certainly, Smartlead is designed for seamless integration with a wide range of tools and platforms. Smartlead offers integration with HubSpot, Salesforce, Pipedrive, Clay, Listkit, and more. You can leverage webhooks and APIs to integrate the tools you use. Try Now!

Email automation FAQs- Smartlead

What type of businesses sees the most success with Smartlead?

No, there are no limitations on the number of channels you can utilize with Smartlead. Our multi-channel infrastructure is designed to be limitless, allowing you to reach potential customers through multiple avenues without constraints.

This flexibility empowers you to diversify your cold email outreach efforts, connect with your audience through various communication channels, and increase your chances of conversion. Whether email, social media, SMS, or other communication methods, Smartlead's multi-channel capabilities ensure you can choose the channels that best align with your outreach strategy and business goals. This way, you can engage with your prospects effectively and maximize the impact of your email outreach.

Email automation FAQs- Smartlead

Do you provide me with lead sources?

Smartlead distinguishes itself from other cold email outreach software by focusing on limitless scalability and seamless integration. While many similar tools restrict your outreach capabilities, Smartlead offers a different approach.

Here's what makes us uniquely the best cold email software:

1. Unlimited Mailboxes: In contrast to platforms that limit mailbox usage, Smartlead provides unlimited mailboxes. This means you can expand your outreach without any arbitrary constraints.

2. Unique IP Servers: Smartlead offers unique IP servers for every campaign it sends out. 

3. Sender Reputation Protection: Smartlead protects your sender reputation by auto-moving emails from spam folders to the primary inbox. This tool uses unique identifiers to cloak all warmup emails from being recognized by automation parsers. 

4. Automated Warmup: Smartlead’s warmup functionality enhances your sender reputation and improves email deliverability by maintaining humanized email sending patterns and ramping up the sending volume. 

5. Multi-Channel Emphasis: Smartlead places a strong emphasis on multi-channel outreach. You can reach your prospects where they are with the LinkedIn outreach feature.   With Smartlead’s cold email automation software, you're always one step ahead in your outreach efforts, enjoying the freedom to scale your initiatives and seamlessly integrate with other tools—all while maintaining a focus on maximizing the impact of your outreach.

Email automation FAQs- Smartlead

How secure is my data with Smartlead?

Ensuring the security of your data is Smartlead's utmost priority. We implement robust encryption methods and stringent security measures to guarantee the continuous protection of your information. Your data's safety is paramount to us, and we are always dedicated to upholding the highest standards of security.

How can I get started with Smartlead?

Email automation FAQs- Smartlead

Getting started with Smartlead is straightforward! Just head over to our sign-up page and follow our easy step-by-step guide. If you ever have any questions or need assistance, our round-the-clock support team is ready to help, standing by to provide you with any assistance you may require. Sign Up Now!

How can I reach the Smartlead team?

Email automation FAQs- Smartlead

We're here to assist you! You can easily get in touch with our dedicated support team on chat. We strive to provide a response within 24 hours to address any inquiries or concerns you may have.

Powerful Automated Email Marketing that Drives Sales.

  • All Features Included
  • No Credit Card Required
  • Free Warmup Included