3.4.8. FOLDING LONG HEADER FIELDS

Each header field may be represented on exactly one line consisting of the name of the field and its body, and terminated by a CRLF; this is what the parser sees. For readability, the field-body portion of long header fields may be "folded" onto multiple lines of the actual field. "Long" is commonly interpreted to mean greater than 65 or 72 characters. The former length serves as a limit, when the message is to be viewed on most simple terminals which use simple display software; however, the limit is not imposed by this standard.

Note: Some display software often can selectively fold lines, to suit the display terminal. In such cases, sender-provided folding can interfere with the display software.