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SMTP Email Error 550 5.1.1 - How to Resolve [SOLVED]

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    Nowadays, no business can do without email; it plays a key role. It’s how we share ideas, close deals, and keep things moving. But sometimes things go wrong, like with the SMTP 550 5.1.1 email error. Let’s figure out what this error is and how to fix it so that your letters always reach the recipient.

    Understanding SMTP email error 550 5.1.1

    This error serves as the digital equivalent of a “Return to Sender” notification, indicating a failure in email delivery through the Simple Mail Transfer Protocol (SMTP), the standard communications protocol for sending email over the Internet.

    When an email is returned with a 550 5.1.1 error, it means that the recipient’s email server cannot recognize the email address provided. This can happen for several reasons: the email address may have been entered incorrectly, the recipient’s email account no longer exists, or there may be problems with the recipient’s mail server.

    Common causes of SMTP email error 550 5.1.1

    SMTP Email Error 550 5.1.1 can occur due to a variety of problems, each of which indicates a fundamental problem in the way email is addressed or routed.

    Invalid recipient email address

    This is one of the most common reasons – when you make a mistake in the email address.

    Problems with the domain name

    If the domain portion of the email address (the section after the @ symbol) is incorrect or no longer exists, emails will not be delivered. This happens when a company changes its name and domain.

    Problems with server configuration

    On the recipient’s side, the mail server may be configured in such a way that it does not recognize or accept emails to a valid address. This may be due to strict filtering rules or a misconfigured server that effectively blocks incoming messages.

    Outdated DNS records

    The Domain Name System (DNS) resolves domain names into IP addresses. If the DNS records for the email recipient’s domain are out of date or set incorrectly, email servers cannot find the correct route to deliver the email, causing transmission to fail.

    Step-by-step solutions to resolve SMTP email error 550 5.1.1

    Regardless of which email provider you use – be it Gmail, Outlook, Yahoo or another digital email service, let’s look at the general steps:

    1. Check your email address carefully

    Make sure there are no typos or errors. It’s easy to misspell a name or misspell a domain, so take another look.

    2. Check your email settings

    Double-check your account settings to see if there are any filters or rules that may be redirecting your emails or blocking them entirely.

    3. Check your server settings

    If you are using an email client (such as Outlook or an email application), make sure your SMTP server settings are correct.

    Here are the SMTP server settings for Gmail, Outlook, and Yahoo, which you might need for configuring email clients or troubleshooting email issues:

    Gmail SMTP Settings

    • Server Address: smtp.gmail.com
    • Port: 587 (for TLS/STARTTLS) or 465 (for SSL)
    • Authentication Required?: Yes
    • Username: Your full Gmail email address (including @gmail.com)
    • Password: Your Gmail password (or an App password if two-factor authentication is enabled)

    Outlook SMTP Settings

    • Server Address: smtp-mail.outlook.com
    • Port: 587
    • Encryption Method: STARTTLS
    • Authentication Required?: Yes
    • Username: Your full Outlook email address (including @outlook.com, @live.com, etc.)
    • Password: Your Outlook password

    Yahoo SMTP Settings

    • Server Address: smtp.mail.yahoo.com
    • Port: 587
    • Encryption Method: STARTTLS
    • Authentication Required?: Yes
    • Username: Your full Yahoo email address (including @yahoo.com)
    • Password: Your Yahoo password

    4. Check your spam filters

    Sometimes outgoing emails may be incorrectly flagged by your account’s spam filters. Make sure your email doesn’t fall into these filters by adjusting them if necessary.

    5. Please note shipping restrictions

    Please be aware of the sending limits set by your email provider. If you send too many emails you can quickly reach your limit.
    Here’s a brief overview of the sending limits for Gmail, Outlook, and Yahoo:


    • Daily Limit: Gmail allows you to send up to 500 emails per day for personal accounts. For G Suite (now Google Workspace) users, this limit increases to 2,000 emails per day.
    • Recipients Limit: Each email can be sent to a maximum of 500 recipients in total for personal accounts and 2,000 for Google Workspace accounts.

    Outlook (Microsoft 365/Office 365)

    • Daily Limit: Outlook.com (for personal use) has a daily limit of 300 emails. For Microsoft 365 or Office 365 business accounts, the limit is much higher, allowing users to send up to 10,000 emails per day.
    • Recipients Limit: The maximum number of recipients per message is 500 for Outlook.com. For Microsoft 365 or Office 365, the limit is 500 recipients for a single email and up to 5,000 recipients per day.

    Yahoo Mail

    • Daily Limit: Yahoo Mail limits users to sending 500 emails per day.
    • Recipients Limit: Each email can have a maximum of 100 recipients.

    6. Contact customer service

    If you have fixed everything, but still receive an error, write to technical support.

    Gmail (Google Workspace)

    • Support Center: Google Workspace users can access support through their admin console, which provides options to contact Google support directly, including phone and email options.
    • Help Center: For free Gmail accounts, Google offers a comprehensive Help Center where you can find answers to common issues and guidance on how to use Gmail features.

    Outlook (Microsoft 365/Office 365)

    • Support Center: Microsoft 365 or Office 365 subscribers can access support directly through their admin portal, where they can find options for email and phone support.
    • Help Center: For free Outlook.com accounts, Microsoft provides a Help Center with troubleshooting guides and FAQs. You can also use the Microsoft Community forums for additional assistance.

    Yahoo Mail

    • Help Center: Yahoo Mail offers a Help Center where you can find answers to common questions and troubleshooting steps for various issues.
    • Customer Care: Direct contact options, including email support, can be limited for free accounts. However, Yahoo does provide a paid subscription service called Yahoo Mail Plus, which offers more direct support options.

    List of common 550 5.1.1 error messages

    Here is a list of all the errors you may receive:

    1. 550 5.1.1 Recipient rejected

      • The recipient’s email server has rejected the message, possibly due to a policy setting or a blacklist.
    2. 550 5.1.1 Recipient address rejected

      • Similar to the above, this message indicates that the recipient’s address is invalid or not recognized by their email server.
    3. 550 5.1.1 Recipient address rejected: User unknown in virtual alias table

      • This error occurs when the recipient’s email server cannot find the email address in its virtual alias table, suggesting the address does not exist.
    4. 550 5.1.1 User unknown

      • A straightforward message indicating that the recipient’s email address is unknown or incorrect.
    5. 550 5.1.1 Mailbox not found

      • The specified mailbox for the recipient does not exist, which could be due to deletion or a typo in the email address.
    6. 550 5.1.1 Invalid mailbox

      • This message suggests that the mailbox format is incorrect or violates the server’s naming conventions.
    7. 550 5.1.1 Mailbox unavailable

      • The recipient’s mailbox is currently unavailable, which could be due to various reasons, including server maintenance or temporary issues.
    8. 550 5.1.1 Unrouteable address

      • The email address cannot be routed correctly, possibly due to an issue with the domain name or DNS settings.
    9. 550 5.1.1 Mailbox temporarily disabled

      • The recipient’s mailbox is temporarily disabled, potentially due to inactivity or account issues.
    10. 550 5.1.1 No such user here

      • This error indicates that the recipient’s email server does not have an account matching the email address provided.

    How the email warm-up service can help you solve the 550 5.1.1 error messages

    warmy dashboard

    Imagine you have a new email account or one that’s collecting dust. If you suddenly start sending a ton of emails, email providers may look at you sideways, thinking you’re up to no good. This is where you hit a wall with errors like the terrible SMTP 550 5.1.1.

    So what do we know about email warming services? This service warms up your mailbox gradually and steadily. It sends emails on your behalf, starting small and then gradually increasing in volume.

    Meet Warmy.io and its team. They take control by automating the entire “getting to know you” step with email providers. They send out emails, make sure they are read, and even respond to them, all to show that your emails are worthy of landing in your inbox. They also monitor for any signs that your emails are ending up in the spam folder, alerting you to make changes.

    Using a service like Warmy.io helps you improve the deliverability of your emails, solving not only the problem with error 550 5.1.1, but also any problems with emails in general, be it technical settings, blacklists or spaces with spam filters. Wormi has highly specialized email deliverability specialists who can easily and quickly solve all your problems.

    We invite you to take a free Email deliverability test and you will immediately see the status of your mailbox and all possible problems. It’s absolutely free


    In wrapping up, tackling the SMTP Email Error 550 5.1.1 isn’t as daunting as it seems. By carefully checking email addresses for typos, ensuring your email settings are spot on, and gradually building your sender’s reputation with services like Warmy.io, you can significantly reduce the chances of hitting this error. Remember, it’s all about taking it step by step and keeping an eye on the details. With these strategies in your toolkit, you’re well on your way to ensuring your emails land right where they should—in the inbox, error-free.


    What is SMTP Email Error 550 5.1.1?

    SMTP Email Error 550 5.1.1 is a common error message indicating that the email you tried to send couldn't be delivered because the recipient's address was not found or is incorrect.

    Why do I keep getting the 550 5.1.1 error?

    This error typically occurs due to misspelled email addresses, outdated contact information, or recipient server issues. It's a signal to check the email address you're sending to and ensure it's correct.

    Can I fix the 550 5.1.1 error on my own?

    Yes, in many cases, you can resolve this error by double-checking the recipient's email address for typos, verifying that the domain name is correct, and ensuring your email server settings are properly configured.

    How can email warm-up services help prevent this error?

    Email warm-up services like Warmy.io gradually increase your email sending activity, helping to build a positive sender reputation. A good reputation reduces the likelihood of your emails being rejected or marked as spam, which can lead to errors like 550 5.1.1.

    What should I do if I still can't resolve the error?

    If you've verified the email address and tried other troubleshooting steps without success, consider reaching out to your email service provider for assistance. They can offer more specific guidance based on their systems and may help identify issues beyond simple address errors.

    Does this error mean I'm on a blacklist?

    Not necessarily. While a 550 5.1.1 error indicates a delivery issue, it doesn't automatically mean you're on a blacklist. However, if you're frequently encountering this and other delivery issues, it might be worth checking your sender reputation and whether your IP has been blacklisted.

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