The UnixFromLine option replaces the pre-V8.7 $l macro. It has two functions:

• It defines the look of the five character "From " header line needed by UUCP software.

• It defines the format of the line that is used to separate one message from another in a file of many mail messages.

The forms of the UnixFromLine option and $l macro are as follows:

Dlformat                        configuration file (V8.6 and earlier) 
O UnixFromLine=format           configuration file (V8.7 and later) 
-OUnixFromLine=format           command line (V8.7 and later) 
define(`confFROM_LINE',`format')    mc configuration (V8.7 and later) 

The format is of type string. Under V8.6 and earlier there was no default for format, so the $l macro always had to be defined. Beginning with V8.7, sendmail first checks to see if the UnixFromLine option was defined and uses that value if it was. Otherwise, it checks to see whether the level of the configuration file is 6 or less. If it is and if the $l macro was defined, it uses that value. Otherwise, it uses the default:

From $g  $d

Here, $g ($g) holds the sender's address relative to recipient, and $d ($d) holds as its value the current date in Unix ctime(3) format.

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

UnixFromLine in UUCP software

UUCP software requires all messages to begin with a header line that looks like this:

From sender   date  remote from <host> 

The sendmail program prefixes such a line to a mail message's headers if the F=U flag (F=U) is set for the delivery agent.^[73] Prior to V8.7, if the local machine supports UUCP, the $l macro must be supplied with "From ", sender, and date:

^[73] Prior to V8.7 this behavior was supported only if UGLYUUCP was defined in conf.h when sendmail was compiled.

DlFrom $g $d

The rest of the information (the remote from <host> ) is supplied by sendmail.

UnixFromLine with mail files

Under Unix, in a file of many mail messages, such as a mailbox, lines that begin with the five characters "From " are used to separate one message from another. This is a convention that is not shared by all MUAs. The sendmail program appends mail messages to files under only two circumstances: when saving failed mail to the user's dead-letter file, and when delivering to a local address that begins with the / character. In appending messages to files, it uses the UnixFromLine ($l) option to define the form of the message separator lines.

For sites that use the Rand MUA (and that do not also use UUCP), the UnixFromLine ($l) option can be defined to be four Ctrl-A characters:

Dl^A^A^A^A
O UnixFromLine=^A^A^A^A