Send & Receive Issues

How to Fix the Message Has Lines Too Long for Transport Error in Outlook

Huma Ashraf Ch Sep 28, 2026 869 views

Question details

The user is encountering a bounce-back SMTP error stating that an email message has lines too long for transport when sending to external recipients.

How to Fix the Email Error: Message Has Lines Too Long for Transport

Product: Microsoft Outlook
Device & OS: not provided
Scenario: Sending an email with deeply nested quotes or complex formatting to an external domain using the Outlook desktop client.
Observed behavior: Internal emails and webmail send successfully, but sending externally via the Outlook client triggers a non-delivery report (NDR) because the message formatting exceeds SMTP line limits.

Before you start

Verify if the issue persists when sending the exact same email via your webmail interface to confirm whether the problem is isolated to your local Outlook desktop client.

Solution 1Recommended

Send a Clean Plain Text Email

Use this method as a quick workaround when deeply nested email replies or hidden HTML formatting causes the transport error.

Often, this SMTP error occurs because copied content or a long chain of replied messages contains corrupted or overly complex HTML coding that Outlook formats incorrectly for external delivery.

Create a new message

Open Outlook and click on 'New Email' in the ribbon. Do not click 'Reply' or 'Forward' on the problematic email thread.

Copy essential text only

Highlight and copy only the essential text from your original draft. Avoid copying quoted headers or complex tables.

Paste as plain text

Right-click inside the body of the newly created email and select 'Keep Text Only' under the Paste Options. Address the email and click 'Send'.

Workaround Successful: Sending clean text strips away the hidden HTML that exceeds standard SMTP line length limits, ensuring successful external delivery.

Solution 2

Test Outlook in Safe Mode

Run Outlook without any third-party add-ins to see if an external plugin is corrupting your outgoing email formatting.

Solution 3

Recreate the Outlook Mail Profile

If the error affects only one specific account within the Outlook client, your local mail profile may be corrupted.

Free Microsoft Office alternative

Switch to a Seamless Office Experience with WPS Office

If you are tired of complex Outlook errors, heavy application updates, and expensive subscriptions, consider simplifying your workflow with WPS Office. It provides a lightweight, highly compatible, and free alternative with a familiar interface for all your document, spreadsheet, and presentation needs.

1. Download the software: Visit the official WPS website to download the free, lightweight installation package.
2. Install quickly: Run the installer and complete the setup process in just a few minutes on Windows, Mac, or Linux.
3. Open existing files: Instantly open, edit, and save your existing Microsoft Office files with perfect formatting retention.

Fully compatible with Microsoft Word, Excel, and PowerPoint formats (.docx, .xlsx, .pptx).Lightweight installation that runs smoothly on all devices without heavily consuming system resources.Built-in robust PDF editing tools combined with classic office applications in one single tabbed window.Familiar user interface ensuring seamless migration without a steep learning curve.

microsoft office alternative - wps office

Frequently Asked Questions

Why does the 'lines too long for transport' error only affect external emails?

Internal Microsoft Exchange servers often process rich text and proprietary HTML formatting natively without issues. However, when sending externally, Outlook must convert the message to standard Internet email format. If deeply nested quotes or corrupt formatting causes a line of code to exceed the maximum character limit set by standard SMTP gateways, the external server rejects it.

Will changing the wrap text settings in Outlook fix this error?

Adjusting the 'Automatically wrap text at character' setting under File > Options > Mail > Message format is frequently suggested. However, it often fails to resolve this specific error if the underlying cause is deeply embedded formatting or long unbreakable links in quoted replies.

What should I do if recreating my Outlook profile doesn't solve the issue?

If local troubleshooting like Safe Mode, plain text sending, and profile recreation all fail, the issue may be server-related. You should collect the complete Non-Delivery Report (NDR) provided in the bounce-back message and forward it to your organization's mail administrator or Microsoft Support to check for problematic transport rules or SMTP configurations.

Outlook & Email Problems