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SMTP Email Error 553 5.1.3 - How to Resolve [SOLVED]

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    Email remains a crucial tool in our digital age, powering communication for businesses and individuals alike. It fosters connections, nurtures leads, and drives sales. But what happens when your meticulously crafted emails vanish into the abyss, never reaching their intended recipients?

    One frequent culprit behind failed deliveries is SMTP Email Error 553 5.1.3. Don’t despair! While frustrating, this error often has a fix.

    This series will delve into the causes of Error 553 5.1.3 and equip you with solutions to keep your email communication flowing smoothly, ensuring your messages land in inboxes, not the dreaded spam folder.

    Deciphering the error: SMTP email error 553 5.1.3 unpacked

    SMTP Email Error 553 5.1.3 is essentially a signal from the email system indicating a problem with the recipient’s address format used in the email sent. This error usually occurs when there’s a typo in the email address, an unsupported character, or a format that the email server fails to recognize as valid. It’s the email system’s way of saying, “I don’t know where to deliver this message because the address doesn’t look right to me.”

    Users encountering this issue might see messages such as:

    • “553 5.1.3 The recipient address <email_address> is not a valid RFC-5321 address.”
    • “Error 553 5.1.3: <email_address>… User address malformed.”
    • “Failed to send; SMTP server error 553 5.1.3 <email_address>… Syntax error in mailbox address.”

    These notifications are the email system’s attempt to notify the sender that the email couldn’t be delivered due to an issue with the format of the recipient’s email address. 

    Root causes: why does SMTP email error 553 5.1.3 occur?

    SMTP Email Error 553 5.1.3 can arise from several factors, primarily related to issues with the email address format being sent to. Understanding these common causes can help in effectively diagnosing and solving the problem:

    Incorrect Email Address

    The most straightforward reason is simply typing the email address incorrectly. This could mean misspelling the address, omitting characters, or including spaces and special characters that aren’t typically part of email formats.

    Improper Email Format

    Some email servers have strict rules about which characters can appear in an email address. Using unsupported characters, even if they’re technically valid in other contexts, can trigger this error.

    Unsupported Characters

    Email addresses must follow a specific format (e.g., user@example.com). Variations that deviate from this standard, such as missing the “@” symbol or the domain part, will lead to an error.

    Misconfigurations in Email Client

    Sometimes, the way an email client (like Outlook or Gmail) is configured can cause it to incorrectly format outgoing email addresses, even if you’ve entered them correctly.

    Issues with Mail Exchange Records

    On the recipient’s side, misconfigured MX records can lead to undeliverable emails, although this typically generates different error codes, it’s worth considering if the format looks correct.

    Troubleshooting guide: resolving SMTP email error 553 5.1.3

    email deliverability

    For Gmail Users

    Verify Email Address Format

    Double-check the recipient’s email address for any typos or formatting errors.

    Check Account Settings

    Go to Settings > See all settings > Accounts and Import. Under “Send mail as,” ensure the email address is correctly formatted and verified.

    Review SMTP Settings

    Ensure that the SMTP server is set to smtp.gmail.com, the port is set to 587 (for TLS) or 465 (for SSL), and that “Use Authentication” is enabled with your correct Gmail address and password.

    For Outlook Users

    Email Address Verification

    As with Gmail, start by verifying the format of the recipient’s email address.

    Adjust Email Account Settings

    Go to File > Account Settings > Server Settings. Then click on Outgoing Mail and confirm that the SMTP settings are correct: server smtp-mail.outlook.com, port 587, and encryption method TLS.

    Ensure Correct Authentication

    In the same settings menu, make sure the option for “My outgoing (SMTP) server requires authentication” is checked, and “Use same settings as my incoming mail server” is selected.

    For Yahoo Users

    Recipient Address Check

    Ensure the email address you’re sending to is free of errors and correctly formatted.

    SMTP Configuration

    Check your SMTP settings by going to Account Info > Account Security > Manage App Passwords. Select your email app and generate a unique app password. Use this app password along with your email address to authenticate your SMTP server.

    SMTP Server Details

    The SMTP server for Yahoo should be set to smtp.mail.yahoo.com, with port 465 (SSL required) or 587 (TLS required).

    The role of email warm-up services

    warmy dashboard

    Email warm-up services play a crucial role in enhancing the deliverability of your emails, significantly reducing the chances of encountering SMTP errors like 553 5.1.3. Services such as Warmy.io are designed to gradually increase the volume of emails sent from a new or recently reset email account, mimicking human-like activity to establish a reputation with email service providers.

    Benefits of Using Email Warm-Up Services:

    1. Builds Sender Reputation. Gradually sending more emails over time helps in building a positive sender reputation, which is crucial for ensuring your emails reach the inbox.

    2. Reduces Email Bounces. By enhancing your sender reputation, warm-up services reduce the likelihood of your emails being bounced or marked as spam.

    3. Prevents Blacklisting. A good sender reputation also helps in preventing your email domain from being blacklisted by major email service providers.

    4. Improves Email Engagement Rates. Emails that land in the inbox are more likely to be opened, read, and clicked on, thereby improving overall engagement rates.

    Warmy.io offers additional tools that complement its warm-up service, further ensuring your emails are delivered successfully:

    • Free Email Deliverability Test. This feature allows you to check how likely your emails are to be delivered to your recipient’s inbox, providing insights on areas for improvement.

    • Blacklist Checks. Warmy.io can check if your email domain has been blacklisted, which is a common cause of email delivery issues.

    • SPF and DMARC Record Generators. Setting up correct SPF (Sender Policy Framework) and DMARC (Domain-based Message Authentication, Reporting, and Conformance) records are essential for email authentication. Warmy.io provides tools to generate these records for free, helping you comply with email security standards and improve deliverability.

    SPF generator


    Addressing SMTP Email Error 553 5.1.3 quickly is crucial for maintaining uninterrupted email communication, crucial for today’s digital interactions. This guide has walked you through practical solutions for popular email platforms and highlighted the preventative benefits of email warm-up services like Warmy.io. By applying these targeted strategies, you can ensure your emails consistently reach their intended recipients, keeping your communication channels open and effective. Take action now to safeguard your email delivery and keep your professional connections strong.

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    What causes SMTP Email Error 553 5.1.3?

    This error typically occurs due to incorrect email address formatting, including typos, unsupported characters, or missing parts of the address. It can also be triggered by misconfigurations in your email client settings.

    How can I prevent SMTP Email Error 553 5.1.3?

    Prevention starts with ensuring all email addresses are correctly formatted before sending. Regularly review and update your email client settings to match your email service provider's recommendations. Using email validation tools can also help catch errors before sending.

    Are there long-term fixes for SMTP Email Error 553 5.1.3?

    Yes, establishing rigorous checks for email address validity and maintaining up-to-date email client configurations serve as long-term solutions. Additionally, implementing email warm-up practices can improve your sender reputation, reducing the likelihood of such errors.

    Can email warm-up services prevent SMTP errors?

    Absolutely. Services like Warmy.io gradually increase your email sending volume, helping to build a positive sender reputation. This can prevent not only SMTP Email Error 553 5.1.3 but other delivery issues as well, by ensuring your emails are recognized as legitimate.

    What should I do if I continue to experience SMTP Email Error 553 5.1.3 despite corrections?

    If the error persists, double-check for any overlooked misconfigurations in your email settings. Consider consulting with your email service provider or seeking assistance from email deliverability experts. Sometimes, external factors, such as server issues on the recipient's end, may also play a role.

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