Murray is of course correct that duplicated headers could be used to fool sorting programs like procmail or filtering programs.
I have an archive of a lot of the spam received on my system in recent years, so I've been grepping through it looking for duplicated from and subject headers. Here's what I've found so far. The URLs below are real, and will fetch you a copy of the spam. Each line tells how many from and subject lines the message has, and "same" means the two subjects are the same. In this tiny sample, every duplicated subject is the same, and the duplicated froms are all similar to each other, and appear to be due to bugs in the spamware, not malicious intent. I dunno what that tells us, other than that whatever attack is enabled by duplicated headers, it doesn't appear to have happened yet. But I do share Mark's concern that it would be unfortunate if there were ways to make significant changes to the way a message renders without breaking a non-silly signature, i.e., one that covers the usual headers and the whole body. R's, John http://spample.iecc.com/uft/22579237 !!! from 2 subj 1 http://spample.iecc.com/trh/22584748 !!! from 1 subj 2 same http://spample.iecc.com/hua/22585805 !!! from 1 subj 2 same http://spample.iecc.com/jaw/22594898 !!! from 1 subj 2 same http://spample.iecc.com/jcf/22594899 !!! from 1 subj 2 same http://spample.iecc.com/kea/22594900 !!! from 1 subj 2 same http://spample.iecc.com/kgi/22594901 !!! from 1 subj 2 same http://spample.iecc.com/ljd/22594902 !!! from 1 subj 2 same http://spample.iecc.com/llm/22594903 !!! from 1 subj 2 same http://spample.iecc.com/mnh/22594904 !!! from 1 subj 2 same http://spample.iecc.com/mpp/22594905 !!! from 1 subj 2 same http://spample.iecc.com/nrk/22594906 !!! from 1 subj 2 same http://spample.iecc.com/ntt/22594907 !!! from 1 subj 2 same http://spample.iecc.com/pxx/22594909 !!! from 1 subj 2 same http://spample.iecc.com/pzr/22594910 !!! from 1 subj 2 same http://spample.iecc.com/qba/22594911 !!! from 1 subj 2 same http://spample.iecc.com/qdv/22594912 !!! from 1 subj 2 same http://spample.iecc.com/rge/22594913 !!! from 1 subj 2 same http://spample.iecc.com/riy/22594914 !!! from 1 subj 2 same http://spample.iecc.com/syh/22594915 !!! from 1 subj 2 same http://spample.iecc.com/sac/22594916 !!! from 1 subj 2 same http://spample.iecc.com/tcl/22594917 !!! from 1 subj 2 same http://spample.iecc.com/teg/22594918 !!! from 1 subj 2 same http://spample.iecc.com/ugo/22594919 !!! from 1 subj 2 same http://spample.iecc.com/uij/22594920 !!! from 1 subj 2 same http://spample.iecc.com/vks/22594921 !!! from 1 subj 2 same http://spample.iecc.com/vmn/22594922 !!! from 1 subj 2 same http://spample.iecc.com/wov/22594923 !!! from 1 subj 2 same http://spample.iecc.com/xrq/22594924 !!! from 1 subj 2 same http://spample.iecc.com/xtz/22594925 !!! from 1 subj 2 same http://spample.iecc.com/yvu/22594926 !!! from 1 subj 2 same http://spample.iecc.com/yxc/22594927 !!! from 1 subj 2 same http://spample.iecc.com/zzx/22594928 !!! from 1 subj 2 same http://spample.iecc.com/zbg/22594929 !!! from 1 subj 2 same http://spample.iecc.com/adb/22594930 !!! from 1 subj 2 same http://spample.iecc.com/afk/22594931 !!! from 1 subj 2 same http://spample.iecc.com/bhe/22594932 !!! from 1 subj 2 same http://spample.iecc.com/bjn/22594933 !!! from 1 subj 2 same http://spample.iecc.com/cli/22594934 !!! from 1 subj 2 same http://spample.iecc.com/cor/22594935 !!! from 1 subj 2 same http://spample.iecc.com/dql/22594936 !!! from 1 subj 2 same http://spample.iecc.com/dsu/22594937 !!! from 1 subj 2 same http://spample.iecc.com/eup/22594938 !!! from 1 subj 2 same http://spample.iecc.com/ewy/22594939 !!! from 1 subj 2 same http://spample.iecc.com/fys/22594940 !!! from 1 subj 2 same http://spample.iecc.com/gab/22594941 !!! from 1 subj 2 same http://spample.iecc.com/gcw/22594942 !!! from 1 subj 2 same http://spample.iecc.com/her/22594943 !!! from 1 subj 2 same http://spample.iecc.com/hga/22594944 !!! from 1 subj 2 same http://spample.iecc.com/iiu/22594945 !!! from 1 subj 2 same http://spample.iecc.com/ild/22594946 !!! from 1 subj 2 same http://spample.iecc.com/jph/22594948 !!! from 1 subj 2 same http://spample.iecc.com/krb/22594949 !!! from 1 subj 2 same http://spample.iecc.com/khk/22594950 !!! from 1 subj 2 same http://spample.iecc.com/ljf/22594951 !!! from 1 subj 2 same http://spample.iecc.com/llo/22594952 !!! from 1 subj 2 same http://spample.iecc.com/mpr/22594954 !!! from 1 subj 2 same http://spample.iecc.com/nrm/22594955 !!! from 1 subj 2 same http://spample.iecc.com/ntv/22594956 !!! from 1 subj 2 same http://spample.iecc.com/owq/22594957 !!! from 1 subj 2 same http://spample.iecc.com/pyy/22594958 !!! from 1 subj 2 same http://spample.iecc.com/pat/22594959 !!! from 1 subj 2 same http://spample.iecc.com/qcc/22594960 !!! from 1 subj 2 same http://spample.iecc.com/qex/22594961 !!! from 1 subj 2 same http://spample.iecc.com/rgf/22594962 !!! from 1 subj 2 same http://spample.iecc.com/ria/22594963 !!! from 1 subj 2 same http://spample.iecc.com/skj/22594964 !!! from 1 subj 2 same http://spample.iecc.com/sme/22594965 !!! from 1 subj 2 same http://spample.iecc.com/tom/22594966 !!! from 1 subj 2 same http://spample.iecc.com/tqh/22594967 !!! from 1 subj 2 same http://spample.iecc.com/usq/22594968 !!! from 1 subj 2 same http://spample.iecc.com/uvl/22594969 !!! from 1 subj 2 same http://spample.iecc.com/vxu/22594970 !!! from 1 subj 2 same http://spample.iecc.com/vzo/22594971 !!! from 1 subj 2 same http://spample.iecc.com/wbx/22594972 !!! from 1 subj 2 same http://spample.iecc.com/wds/22594973 !!! from 1 subj 2 same http://spample.iecc.com/xfb/22594974 !!! from 1 subj 2 same http://spample.iecc.com/yhv/22594975 !!! from 1 subj 2 same http://spample.iecc.com/yje/22594976 !!! from 1 subj 2 same http://spample.iecc.com/zlz/22594977 !!! from 1 subj 2 same http://spample.iecc.com/zni/22594978 !!! from 1 subj 2 same http://spample.iecc.com/apc/22594979 !!! from 1 subj 2 same http://spample.iecc.com/asl/22594980 !!! from 1 subj 2 same http://spample.iecc.com/cyk/22594983 !!! from 1 subj 2 same http://spample.iecc.com/cas/22594984 !!! from 1 subj 2 same http://spample.iecc.com/dcn/22594985 !!! from 1 subj 2 same http://spample.iecc.com/dsi/22594986 !!! from 1 subj 2 same http://spample.iecc.com/eur/22594987 !!! from 1 subj 2 same http://spample.iecc.com/lxp/22595001 !!! from 1 subj 2 same http://spample.iecc.com/iwr/22595338 !!! from 2 subj 1 http://spample.iecc.com/lct/22596053 !!! from 1 subj 2 same http://spample.iecc.com/kzp/22619085 !!! from 1 subj 2 same http://spample.iecc.com/lpk/22619086 !!! from 1 subj 2 same http://spample.iecc.com/ypw/22622689 !!! from 2 subj 1 http://spample.iecc.com/ppv/22626347 !!! from 1 subj 2 same http://spample.iecc.com/lna/22626634 !!! from 1 subj 2 same http://spample.iecc.com/qsk/22626692 !!! from 2 subj 1 http://spample.iecc.com/kaa/22628715 !!! from 2 subj 1 http://spample.iecc.com/edn/22647571 !!! from 1 subj 2 same http://spample.iecc.com/zpf/22649547 !!! from 1 subj 2 same http://spample.iecc.com/jaa/22650694 !!! from 1 subj 2 same http://spample.iecc.com/kps/22666352 !!! from 1 subj 2 same http://spample.iecc.com/lvr/22666355 !!! from 1 subj 2 same http://spample.iecc.com/vuo/22667011 !!! from 1 subj 2 same http://spample.iecc.com/wxj/22667012 !!! from 1 subj 2 same http://spample.iecc.com/wzr/22667013 !!! from 1 subj 2 same http://spample.iecc.com/ubi/22667352 !!! from 1 subj 2 same http://spample.iecc.com/lxd/22668927 !!! from 1 subj 2 same http://spample.iecc.com/lzm/22668928 !!! from 1 subj 2 same http://spample.iecc.com/mbh/22668929 !!! from 1 subj 2 same http://spample.iecc.com/oqm/22674006 !!! from 1 subj 2 same http://spample.iecc.com/ibk/22674042 !!! from 1 subj 2 same http://spample.iecc.com/eur/22675628 !!! from 2 subj 1 http://spample.iecc.com/oxu/22678416 !!! from 2 subj 1 http://spample.iecc.com/avr/22678636 !!! from 1 subj 2 same http://spample.iecc.com/bxm/22678637 !!! from 1 subj 2 same http://spample.iecc.com/aci/22682408 !!! from 2 subj 1 http://spample.iecc.com/yps/22683752 !!! from 1 subj 2 same Regards, John Levine, [email protected], Primary Perpetrator of "The Internet for Dummies", Please consider the environment before reading this e-mail. http://jl.ly _______________________________________________ NOTE WELL: This list operates according to http://mipassoc.org/dkim/ietf-list-rules.html
