# Exim filter
# Version 0.2
# Released to the public domain by Jeremy Malcolm <Jeremy@Malcolm.id.au>
#
# Will reject outgoing emails that claim to include attachments, but don't.
# Enable this filter by setting its path in system_filter in exim[4].conf.
# Be sure to set your sending domain/s at line 18 below!
#
# Test with /usr/sbin/sendmail -bF fta.filter < test-message
#
# Requirements:
# - Exim 3.2 or higher
# - An alias "no-attachment" at your domain pointing to /dev/null
#
# Limitations:
# - Will misfire on an email like this:
#   > I'm attaching a draft. - Bob
#   Thanks for that, Bob. - Steve
#
# Changelog:
# - 0.1, 6 September 2010: Initial release
# - 0.2, 2 March 2011: No longer misfires on multipart/signed emails.
#

if
   error_message or
   foranyaddress $recipients ($thisaddress is no-attachment@$sender_address_domain) or
   $sender_address_domain does not match "(yourdomain\.tld|yourotherdomain\.tld)"
then
  finish
elif
   $message_body matches "(((is|find|['|ha]ve) attached)|(([a']m|[a']re) (attaching|forwarding))|((the|an) attachment))" and
   $h_content-type does not contain multipart/mixed and
   $message_body does not contain multipart/mixed
then
  fail "<<Forgot attachment>>Please check that you have not forgotten an attachment to this message.\nTo force delivery, BCC \"no-attachment@$sender_address_domain\"."
endif