fixup! add mail-from option

refine usage wording

Author: rhansen

ddclient.conf.in

@@ -25,7 +25,9 @@ daemon=300                      # check every 300 seconds
 syslog=yes                      # log update msgs to syslog
 mail=root                       # mail all msgs to root
 mail-failure=root               # mail failed update msgs to root
-# mail-from=root                # send mail from root, by default unset and handled by system sendmail
+# mail-from=root                # set the email "From:" header to "root".  If
+                                # unset (the default) or empty, the from address
+                                # depends on your system's default behavior.
 pid=@runstatedir@/ddclient.pid  # record PID in file.
 # postscript=script             # run script after updating.  The new IP is
                                 # added as argument.

ddclient.in

@@ -1428,7 +1428,7 @@ my @opt = (
     ["max-warn",          "=i", "--max-warn=<max>       : log at most <max> warning messages for undefined IP address"],
     ["mail",              "=s", "--mail=<address>       : e-mail messages to <address>"],
     ["mail-failure",      "=s", "--mail-failure=<addr>  : e-mail messages for failed updates to <addr>"],
-    ["mail-from",         "=s", "--mail-from=<addr>     : send status e-mail messages from <addr>"],
+    ["mail-from",         "=s", '--mail-from=<addr>     : set the "From:" header in e-mail messages to <addr> if non-empty'],
     ["exec",              "!",  "--{no}exec             : do {not} execute; just show what would be done"],
     ["debug",             "!",  "--{no}debug            : print {no} debugging information"],
     ["verbose",           "!",  "--{no}verbose          : print {no} verbose information"],