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I am suddenly being told that my emails contain 'bare line feed characters' that cannot be sent.

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  • Last reply by Janet1593

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I have had no problems sending new messages or replying to old ones on Thunderbird until this morning. My emails go through Thunderbird to an Office 365 server, and I am getting this message back from that server: "Your message contains invalid characters (bare line feed characters). This error occurs when the email program or device used to create or send an email message adds bare line feed characters into the message. When bare line feed characters are included in a message, the SMTP protocol chunking feature is required to transmit the message between email servers. Chunking uses the SMTP protocol BDAT command, but the recipient's email server doesn't support the BDAT command. To fix the issue, the sender should send the message using an email program or device that doesn't add bare line feed characters to messages. Most modern email programs don't add bare line feed characters."

This problem seems to affect one mail box only in Thunderbird on one computer. I have Thunderbird on two PCs (one Windows 7, one Windows 10), and each has three mail boxes. There doesn't seem to be any problem on the Windows 10 machine (emails go through just fine), and I am able to send emails from two of the three accounts on the Windows 7 machine. I have rebooted but that didn't help.

Does anyone know what could be causing this problem and what I should do? Many thanks!

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re :I have Thunderbird on two PCs

Are you using the most up to date version 68.5.0 on both PC's ?

Regarding the email you sent that failed.... Did the email have an attachment? If yes, does it send ok if you remove the attachment?

Was the email sent to only one recipient? If no, were the email addresses added one per 'TO' field ? OR did you copy the email addresses from a text file and paste all into one 'TO' field?


Some additional info I located on the topic: Usually each line of characters in an email message ends with a carriage return followed by a line feed (CR LF). A bare line feed is a line feed (LF) character that is not immediately preceded by a carriage return (CR) character. In other words, instead of a line ending with CR LF, it ends with only LF.

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Thank you very much for taking the time to explain what the bare line feed was & providing the links. In the meantime, the problem has somehow resolved itself. There was still a problem after I rebooted, but a couple of hours later everything was back to normal. Hopefully it will stay that way!

 In response to the query, no there was not an attachment: in fact the original message that failed was very short and uncomplicated, and went only to the writer of the email to which I was replying.
 Thank you very much again!

Modified by Janet1593

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