cPanel: message has lines too long for transport

A “Bug” has appeared in the recent update to cPanel affecting sending email from the server for many people. Users are experiencing bounce emails indicating that the “message has lines too long for transport”.

The issue appears to be due to an update to EXIM, which has forced cPanel to also do an update which limits the maximum line length in an SMTP transport.

The problem is that PHP Mail and many other packages do not split lines up, meaning any large, or particularly HTML e-mails will immediately suffer from this issue. It has also been seen to affect emails sent from outlook too.

When this situation occurs the sender will usually receive a typical bounce email with the subject:

Subject: Mail delivery failed: returning message to sender

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

message has lines too long for transport

Action: failed

The main problem seems to be that cPanel have set this limit ridiculously low by default, just a mere 2048 in length, and while this setting can now be edited as of the latest version unfortunately this issue is affecting everyone, managed or unmanaged.

So customers on managed hosting using a provider such as GoDaddy cannot edit this value themselves, and worse; GoDaddy (amongst others) are actively refusing to modify these limits meaning lots of websites are now failing to send emails correctly.

If you are affected by this issue and your hosting provider will not increase this limit, your only choice will be to switch hosting provider. We would be happy to take you on board if you contact us.

How to fix “message has lines too long for transport”

If you are able to access WHM and Exim Configuration then you are in luck, you can edit this value from your WHM interface.

1. Login to your WHM interface.
2. Navigate to Service Configuration / Exim Configuration Manager.
   
3. under Basic Editor / Mail tabs scroll to the bottom or search for Maximum line length for SMTP transports.
   
4. Change this value to something higher, we have been told that setting this to the maximum of 1,000,000 is fine and is what we have done.

Author: Dean WilliamsProfessional PHP Web Developer with expertise in OpenCart Web Development, WordPress Web Development, Bespoke Systems - also a seasoned Linux Server Administrator.

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