When sending emails, you may encounter a delivery failure due to a technical issue called a "bare LF" (Line Feed).
This occurs when an email message contains a Line Feed (\n) character without a preceding Carriage Return (\r). According to RFC 2821, all lines in email messages must be properly terminated with a CRLF sequence (\r\n). If a message contains only a bare LF (\n), most mail servers will reject it as invalid.
RFC 2821 explicitly states:
"SMTP commands and, unless altered by a service extension, message data, are transmitted in 'lines'. Lines consist of zero or more data characters terminated by the sequence ASCII character 'CR' (hex value 0D) followed immediately by ASCII character 'LF' (hex value 0A). This termination sequence is denoted as <CRLF> in this document. Conforming implementations MUST NOT recognize or generate any other character or character sequence as a line terminator."
"In addition, the appearance of 'bare' 'CR' or 'LF' characters in text (i.e., either without the other) has a long history of causing problems in mail implementations and applications that use the mail system as a tool. SMTP client implementations MUST NOT transmit these characters except when they are intended as line terminators and then MUST, as indicated above, transmit them only as a <CRLF> sequence.
Since our mail servers strictly adhere to this standard, any email that does not comply will be rejected, resulting in a 451 error.
If you experience email delivery failures due to bare LFs, follow these steps to resolve the issue:
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