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 in this DOCUMENT.

Conforming implementations MUST NOT recognize or generate any other character or character sequence as a line terminator. Limits MAY be IMPOSED on line lengths by servers.

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 sequence.

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 in this document.

Conforming implementations MUST NOT recognize or generate any other character or character sequence as a line terminator. Limits MAY be imposed on line lengths by servers.

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 sequence.