554 Rejected
If a script running on event rejects a message without specifying an error message, this error is issued.
554 Rejected - Message containing bare LF's.
According to the SMTP specification, every line in an email message should be separated by the ASCII-codes 13 and 10 - carriage return (CR) and line feed (LF). Some spammers and incorrectly working software sends messages which are not correctly formatted. Use this setting to reject these messages. Please note that legitimate email might have incorrectly formatted line endings, if the sending software contains bugs.
If you who are a developer receive this problem, confirm that each line of your email message (both header and body) is ended with a carriage return and a line feed, and not just a line feed. How to do this depends on what programming language you are working with. In .C++, C#, and PHP add \r\n to the end of every line. In Visual Basic, add vbNewLine or vbCRLF.
On Windows, the default line separator is CRLF. On Linux and UNIX, the default separator is only LF. However, when sending an email message from a Linux/UNIX system, CRLF must always be used. Some email servers under Linux (such as Postfix) automatically replaces LF with CRLF. Hence, setting the line separator in the email to CRLF will cause it to be changed to CRCRLF.
554 Tagged as Spam by SpamAssassin
If an email message is rejected by SpamAssassin, this error message is issued.