Many Unix MUAs, as well as some transmittal systems such as UUCP, require that a mail-message header begin with a line that begins with the five-character sequence "From ". All other header lines must adhere to the RFC2822 standard and be delimited with a colon:

From jqp@Washington.DC.gov Mon Jan 01 12:35:25 2001
Return-Path: <jqp@Washington.DC.gov>
Date: Mon, 01 Jan 2001 12:35:15 PDT
From: jqp@Washington.DC.gov (John Q Public)

If you don't set the SaveFromLine option, the first line in the previous example is stripped out by sendmail. The SaveFromLine option prevents this because it tells sendmail to keep header lines that begin with the five characters "From ". But note that it also causes this header to no longer be recognized as a header.

The forms of the SaveFromLine option are as follows:

O SaveFromLine=bool               configuration file (V8.7 and later) 
-OSaveFromLine=bool               command line (V8.7 and later) 
define(`confSAVE_FROM_LINES',bool)    mc configuration (V8.7 and later) 
-s                                command-line shorthand (not recommended) 
Ofbool                            configuration file (deprecated) 
-ofbool                           command line (deprecated) 

The optional argument bool is of type Boolean. If bool is missing, this option becomes true (the "From " line is saved). If the entire option is missing, it defaults to false (neither save the "From " line nor recognize it as a header).

The SaveFromLine option is not safe. If specified from the command line, it can cause sendmail to relinquish its special privileges.