exim pipe transport, notmuch insert and mbox-style messages

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+Date: Sat, 22 Nov 2014 09:28:51 +0000\r
+From: Edward Betts <edward@4angle.com>\r
+To: notmuch@notmuchmail.org\r
+Subject: exim pipe transport, notmuch insert and mbox-style messages\r
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+\r
+My mail arrives on a Debian machine running exim. It was being filtered\r
+by procmail then piped into 'notmuch insert'. This was generating the\r
+single-message mbox warning:\r
+\r
+> Warning: ...  is an mbox containing a single message,\r
+> likely caused by misconfigured mail delivery.  Support for single-message\r
+> mboxes is deprecated and may be removed in the future.\r
+\r
+I thought it was a problem with procmail delivering mbox style messages to\r
+pipes, so I switched to maildrop. Same problem. This warning is produced\r
+because there is an mbox-style From_ line before the first header line. Here\r
+is an example:\r
+\r
+> From MAILER-DAEMON Fri Jul  8 12:08:34 2011\r
+\r
+The man page for maildrop says this style of message isn't supported, but it\r
+doesn't detect and warn about them. It will pipe them into commands without\r
+removing the From_ line.\r
+\r
+Reading the exim documentation for pipe transports I found the message_prefix\r
+option, which is by default is set like this:\r
+\r
+> message_prefix = \\r
+>   From ${if def:return_path{$return_path}{MAILER-DAEMON}}\\r
+>   ${tod_bsdinbox}\n\r
+\r
+This means that exim turns all messages into mbox style messages before\r
+delivering them to a pipe. The justification given in the documentation is\r
+"This is required by the commonly used /usr/bin/vacation program."\r
+\r
+The fix is to unset the exim message_prefix option for delivery to maildrop.\r
+Here is an example of the Debian exim maildrop_pipe transport with a blank\r
+message_prefix to stop the From_ line being added before the message is piped\r
+to maildrop.\r
+\r
+> maildrop_pipe:\r
+>   debug_print = "T: maildrop_pipe for $local_part@$domain"\r
+>   driver = pipe\r
+>   path = "/bin:/usr/bin:/usr/local/bin"\r
+>   command = "/usr/bin/maildrop"\r
+>   message_prefix =\r
+>   message_suffix =\r
+>   return_path_add\r
+>   delivery_date_add\r
+>   envelope_to_add\r
+\r
+The same fix could be applied for procmail pipe or a pipe from exim to\r
+'notmuch insert'.\r
+\r
+I submitted a Debian bug for exim4-config with my change as a patch. The\r
+maintainer has excepted my patch and uploaded a release of exim4-config with\r
+the fix to Debian experimental. \r
+\r
+https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=769396\r
+\r
+I wonder if 'notmuch insert' could be modified to detect and drop the From_\r
+line before writing the message to disk and index it. It could do that\r
+silently or with a warning.\r
+\r
+-- \r
+Edward.\r