Summary
The 'Line Too Long' Docomo.ne.jp bounce issue is caused by exceeding the maximum line length limit in email messages, as defined by RFC 5322 (998 characters, ideally staying under 78). This can stem from various factors including missing CR/LF characters, incorrect character encoding (especially for non-ASCII characters), long inline styles, and poorly structured HTML. Receiving systems may enforce strict line length rules, though some disable this, potentially breaking email designs. Resolving the issue involves ensuring correct character encoding (UTF-8, quoted-printable or base64), proper CR/LF encoding, refactoring HTML, using CSS for styling instead of inline styles, reviewing email headers, and adjusting MTA settings with caution.
Key findings
- Line Length Limit: Exceeding RFC 5322's maximum line length of 998 characters (ideally under 78) is the core cause.
- Encoding Problems: Incorrect character encoding (UTF-8), especially with non-ASCII, and failure to use quoted-printable/base64 when needed.
- CR/LF Issues: Missing or improper Carriage Return/Line Feed (CR/LF) characters.
- HTML Structure: Poor HTML structure leading to very long lines, as well as long inline styles contributing to the problem.
- Receiving System Variance: Receiving systems vary in line length enforcement strictness.
- Header Length: Long lines in email headers (Subject, Received, etc.) trigger the error.
- MTA Settings: Misconfigured MTA settings or unintended consequences of disabled enforcement.
Key considerations
- Encoding: Ensure correct character encoding (UTF-8) and use quoted-printable or base64 for non-ASCII characters and long lines.
- CR/LF Encoding: Ensure correct CR/LF insertion and encoding.
- HTML Review: Review and refactor HTML code for structure and length, and avoid long inline styles.
- Header Check: Examine email headers for excessively long lines.
- MTA Configuration: Adjust MTA settings carefully, being aware of potential impacts on email design.
- Limit Code Clutter: Keep code clean and within limits by avoiding long lines that exceed the maximum character limit.
- Regular Testing: Test your emails with different email clients and systems to check for compatibility and rendering issues.
What email marketers say
7 marketer opinions
The 'Line Too Long' Docomo.ne.jp bounce issue is primarily caused by exceeding the maximum line length limit in email headers or the email body, as specified by RFC 5322. This limit is typically 998 characters, though keeping lines under 78 characters is recommended for broader compatibility. Contributing factors include improper character encoding (especially with non-ASCII characters), long inline styles, poorly structured HTML, and misconfigured MTA settings. Solutions involve using correct character encoding (UTF-8), applying quoted-printable or base64 encoding for long lines or non-ASCII characters, refactoring HTML to avoid long lines, using CSS for styling instead of inline styles, reviewing email headers for excessive lengths, and adjusting MTA settings with caution.
Key opinions
- Line Length Limit: Exceeding the maximum line length of 998 characters (ideally under 78) as per RFC 5322 causes the error.
- Encoding Issues: Incorrect character encoding (especially with non-ASCII) and failure to use quoted-printable or base64 encoding for long lines.
- HTML Structure: Poor HTML structure leading to extremely long lines of code.
- Inline Styles: Overuse of long inline styles contributes to the problem.
- Header Length: Unusually long lines in email headers (Subject, Received, etc.) trigger the error.
- MTA Configuration: Misconfigured MTA settings for line length enforcement.
Key considerations
- Character Encoding: Ensure correct character encoding (UTF-8) and proper encoding of long lines and non-ASCII characters.
- HTML Refactoring: Review and refactor HTML code to avoid long lines, using CSS for styling and proper nesting.
- Header Review: Examine email headers for unusually long lines, especially in fields like 'Subject' or 'Received.'
- MTA Settings: Adjust MTA settings carefully, considering potential design issues caused by forced linebreaks.
- Code Cleaning: Keep code clean and within limits by avoiding long lines that exceed the maximum character limit.
Marketer view
Email marketer from Email Server Forum recommends checking and adjusting the mail transfer agent (MTA) settings to ensure that line length enforcement is properly configured or disabled if necessary, but with caution to avoid breaking email design.
17 Aug 2021 - Email Server Forum
Marketer view
Email marketer from Mailjet suggests examining the email's headers for unusually long lines, particularly within fields like 'Subject' or 'Received.' Encoding issues here can sometimes lead to this error.
30 Jan 2025 - Mailjet
What the experts say
4 expert opinions
The 'Line Too Long' Docomo.ne.jp bounce issue arises from exceeding the RFC 5322 line length limits (998 characters), often due to improper CR/LF encoding or incorrect handling of non-ASCII characters. Encoding issues are a primary cause. Some receiving systems have strict line length enforcement, while others disable it, risking email design issues. Diagnosing the issue requires examining the email's encoding and structure.
Key opinions
- CR/LF Encoding: Improper CR/LF encoding leads to lines exceeding the character limit (998).
- Non-ASCII Characters: Use of non-ASCII characters without proper quoted-printable or base64 encoding triggers the error.
- RFC 5322 Violation: Exceeding RFC 5322 line length limits in headers or body causes the bounce.
- Receiving System Enforcement: Strict line length enforcement on the receiving end, not always sender's fault.
- MTA Config Variability: Some MTAs disable line length enforcement, potentially breaking email designs.
Key considerations
- Encoding: Use proper character encoding (UTF-8) and encode non-ASCII characters with quoted-printable or base64.
- Line Length: Ensure email lines, especially headers and body content, adhere to RFC 5322 limits.
- Email Inspection: Send a copy of the problematic email to yourself to inspect its encoding and structure.
- MTA Configuration Awareness: Be aware of how the receiving system handles line length enforcement.
Expert view
Expert from Email Geeks recalls that the error means the email isn't properly encoding a CR/LF at the required number of characters (998).
9 Jun 2024 - Email Geeks
Expert view
Expert from Email Geeks explains that if non-ascii characters are used, you almost certainly need to be using quoted-printable or base64 content encoding. Also you should send a copy of that mail to somewhere you can see it, so you can see what was sent and how it's encoded then diagnose from there.
22 Sep 2023 - Email Geeks
What the documentation says
3 technical articles
The 'Line Too Long' Docomo.ne.jp bounce issue arises from exceeding the 998-character line limit, as defined by RFC 5322 for Internet Message Format. This is frequently caused by missing CR/LF characters, encoding problems, or improper handling of attachments. Solutions involve adhering to the line length limits, ensuring correct MIME encoding, and addressing issues related to attachments.
Key findings
- Line Length Exceeded: Email message line exceeds the allowed character limit (usually 998 characters).
- Missing CR/LF: Often caused by missing Carriage Return/Line Feed (CR/LF) characters.
- Encoding Issues: Encoding issues in message body or headers lead to the error.
- Attachment Handling: Improper handling of attachments can cause the 'Line Too Long' error.
- RFC 5322 Standard: Each line of characters must be no more than 998 characters and ideally should be no more than 78 characters.
Key considerations
- CR/LF Insertion: Ensure proper insertion of Carriage Return/Line Feed (CR/LF) characters.
- MIME Encoding: Ensure correct MIME encoding to handle long lines.
- Line Breaking: Break long lines to adhere to the character limit.
- Attachment Review: Check for and resolve any issues related to attachments.
- Compatibility: Adhering to shorter line lengths (78 characters) ensures compatibility across different email systems.
Technical article
Documentation from RFC Editor details the Internet Message Format. It specifies that each line of characters MUST be no more than 998 characters, and SHOULD, be no more than 78 characters, excluding the CRLF. This ensures compatibility across different email systems.
23 Oct 2024 - RFC Editor
Technical article
Documentation from Microsoft explains that 'Line Too Long' error appears due to exceeded character limits in the message body or headers. Encoding issues and improper handling of attachments can cause this. It recommends breaking long lines and ensuring correct MIME encoding.
4 Jun 2023 - Microsoft
How are email bounce rates calculated and what is considered a good bounce rate?
How can I troubleshoot email bounce issues effectively in Email Geeks?
How do I troubleshoot email bounce messages?
What causes '550 relaying denied' bounce errors and how to resolve them?
What causes bounces related to Spamhaus SBL-XBL database and how to troubleshoot?
What causes high bounce rates during IP warming, and how can they be fixed?
