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SMTP Email Error 354 - How to Resolve [SOLVED]

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    SMTP Email Error 354 is a typical problem reported by consumers when sending emails. Understanding their subtleties and how they manifest is critical for effective troubleshooting. This error takes many forms, frequently disturbing the normal flow of electronic communication. Imagine writing a crucial email only to be prevented by a cryptic error message. This article goes into the complexities of SMTP Email Error 354, explaining its appearance and providing practical alternatives for resolution.

    SMTP Email Error 354 typically appears as a response from the mail server during the email transmission process. It may display as a numeric error code accompanied by a brief message or explanation. For example:

    Error 354: Start mail input; end with <CRLF>.<CRLF>

    This error message signifies that the server is ready to accept the email content but requires proper termination with “<CRLF>.<CRLF>” (carriage return, line feed, period, carriage return, line feed). Depending on the email client or application being used, the error message may vary slightly in format and wording, but the essence remains consistent – indicating a specific issue encountered during email transmission.

    Common causes of SMTP email error 354

    Network Connectivity Issues

    Poor internet connection or network disturbances might impede communication between email client and SMTP server, resulting in Error 354.

    Firewall or Antivirus Blocking SMTP Traffic

    Overly restrictive firewall or antivirus settings can block outgoing SMTP traffic, prohibiting successful email transmission.

    Incorrect SMTP Server Settings

    Misconfigured SMTP Server Settings: Incorrect server address, port number, or login credentials can cause Error 354 during email sending.

    Oversized Email Attachments

    Sending emails with large attachments that exceed the size limits specified by the SMTP server or email provider can result in Error 354.

    Server Overload or Resource Constraints

    Error 354 may occur due to server overload, resource constraints, or temporary challenges with the SMTP server’s capacity to handle incoming emails, particularly during peak usage times.

    Step-by-step solutions to resolve SMTP email error 354

    For Gmail

    1. Adjusting SMTP Server Settings:
      • Access Gmail account settings and ensure SMTP server details (server address, port, encryption method) are correctly configured.
    2. Checking Network Connection:
      • Verify that your device is connected to a stable internet connection to ensure uninterrupted communication with Gmail’s SMTP server.
    3. Verifying Firewall or Antivirus Settings:
      • Temporarily disable firewall or antivirus software to check if they are blocking SMTP traffic. If so, adjust settings to allow outgoing email communication.

    For Outlook

    1. Updating SMTP Port Settings:
      • Navigate to Outlook account settings and ensure that the correct SMTP port (usually 587 or 465) is configured.
    2. Ensuring Server Authentication:
      • Confirm that SMTP server authentication settings are enabled and correct authentication credentials are provided.
    3. Testing Email Sending on Alternate Networks:
      • Try sending the email from a different network to determine if the issue is specific to your current network setup.

    For Yahoo

    1. Clearing Outbound Email Queue:
      • Check for any stuck emails in the Outbox and remove them. Sometimes, pending emails can cause SMTP errors.
    2. Authenticating SMTP Server Credentials:
      • Ensure that the SMTP server credentials (username and password) configured in Yahoo Mail settings are accurate.
    3. Reviewing Email Attachment Size Limits:
      • Confirm that the size of email attachments complies with Yahoo’s attachment size limits to avoid triggering SMTP errors.

    Variations of SMTP email error 354

    1. Incomplete Message Error:

      • This variation occurs when the email message is not properly terminated with “<CRLF>.<CRLF>”, as required by the SMTP protocol. It indicates that the email content was not successfully transmitted to the SMTP server.
    2. Connection Timeout Error:

      • Error 354 can occur if the connection between the email client and the SMTP server times out before the email transmission is completed. This could be due to a network issue or a server outage.
    3. Authentication Failure:

      • If the SMTP server rejects the email transmission owing to invalid or illegal authentication credentials, Error 354 with an authentication failure message may appear.
    4. Attachment Size Limit Exceeded:

      • Sending emails with attachments larger than the SMTP server’s permitted size limit can result in Error 354. This variation indicates that the email was rejected due to large attachments.
    5. Server Capacity Reached:

      • During periods of heavy server demand or resource limits, the SMTP server may fail to handle inbound emails, resulting in Error 354. This variation indicates that the server’s capacity has been reached, and email transmission is momentarily suspended.

    Resolving SMTP email error 354 with Warmy.io

    warmy dashboard

    Email warm-up services such as Warmy.io are essential for optimizing email deliverability and resolution of SMTP Email Error 354. Warmy.io helps evaluate your emails’ deliverability by checking on sender reputation, content of the email, and behavior of the recipient.

    This digital tool helps in identifying potential deliverability issues that could cause SMTP error. Furthermore, Warmy.io checks various email blacklists to find if your domain or IP address is listed for spam and abusive behavior, allowing you to take prompt action to de-list and improve email deliverability.

    In addition, Warmy.io checks SPF, DKIM, and DMARC proper configuration status to prevent your brand and emails from extinction while increasing email safety. They also offer an email deliverability test free plan for assessing the effectiveness of your email campaign and generating suggestions for improving deliverability to prevent SMTP 354 errors.

    Lastly, Warmy.io has an SPF checker and DMARC record generator to facilitate the creation and configuration of these two email authentication mechanisms to enhance email verification while preventing SMTP errors.


    To summarize, addressing SMTP Email Error 354 necessitates a comprehensive approach that includes a recapitulation of key solutions such as improving email deliverability, verifying authentication settings, and checking blacklist status.” The significance of careful troubleshooting cannot be emphasized, as it guarantees that all potential problems are discovered and properly addressed.

    Using services like Warmy.io can significantly improve email management by giving the tools and insights needed to optimize email practices and prevent future mishaps.

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