Index: lib/Mail/SpamAssassin/Conf.pm
===================================================================
--- lib/Mail/SpamAssassin/Conf.pm	(revision 592615)
+++ lib/Mail/SpamAssassin/Conf.pm	(working copy)
@@ -54,13 +54,14 @@
 B<NOTE:> if the C<#> character is to be used as part of a rule or
 configuration option, it must be escaped with a backslash.  i.e.: C<\#>
 
-Whitespace in the files is not significant, but please note that starting a
-line with whitespace is deprecated, as we reserve its use for multi-line rule
-definitions, at some point in the future.
+Whitespace in the files is not significant.  Multi-line settings are
+supported via putting a C<\> at the very end of a line; the next
+non-empty line (a line containing something other than whitespace)
+will be added to the end of the continued line, with the continuing
+line's leading whitespace stripped.  The continuing line can also end
+in a C<\>, in which case it too will be continued by the next
+non-empty line.
 
-Currently, each rule or configuration setting must fit on one-line; multi-line
-settings are not supported yet.
-
 File and directory paths can use C<~> to refer to the user's home
 directory, but no other shell-style path extensions such as globing or
 C<~user/> are supported.
Index: lib/Mail/SpamAssassin/Conf/Parser.pm
===================================================================
--- lib/Mail/SpamAssassin/Conf/Parser.pm	(revision 592615)
+++ lib/Mail/SpamAssassin/Conf/Parser.pm	(working copy)
@@ -249,6 +249,36 @@
   while (defined ($line = shift @conf_lines)) {
     local ($1);         # bug 3838: prevent random taint flagging of $1
 
+    # Line continuation via having a '\' at the end of a line; leading
+    # whitespace of continuing line is ignored.  Empty lines are
+    # discarded, with the first non-empty line following the continued
+    # line being used to continue it, but comments are not discarded.
+    while ($line =~ /\\$/) {
+      my $cont;
+      unless (defined ($cont = shift @conf_lines)) {
+        die "config: line '$line' in file $self->{currentfile} ends in \\, " .
+          "but is last element in \@conf_lines";
+      }
+
+      next if ($cont =~ /^\s*$/);
+      $line =~ s/\\$//;
+
+      if ($cont =~ /^file start /) {
+        $cont =~ s/^file start //;
+        die "config: line '$line' in file $self->{currentfile} ends in \\ " .
+          "and continues into the start of file $cont; impossible.";
+      }
+      elsif ($cont =~ /^file end /) {
+        warn "config: line '$line' in file $self->{currentfile} ends in \\, " .
+          "but is last line in the file";
+        unshift(@conf_lines, $cont);
+        unshift(@conf_lines, "");
+        last;
+      }
+      $cont =~ s/^\s*//g;
+      $line .= $cont;
+    }
+
     # bug 5545: used to support testing rules in the ruleqa system
     if ($keepmetadata && $line =~ /^\#testrules/) {
       $self->{file_scoped_attrs}->{testrules}++;