Attachments not being recognized by mailscanner

[A&M ImpacT [W. Kranenborg]]

Dear mailscanner users,

We have a 64-bit server with mailscanner 4.46.2, spamassassin 3.1.3 and
sendmail 8.13.5.

We have a problem with this set-up and we don't know the reason. The
problem is that mailscanner doesn't recognize some attachments so the
binary code of the attachments is shown in the body of the message.
Spamassassin detects a lot of strange characters and gives it a very
high score so the message is marked as spam.
An example message:

-------------------------------------

Here is the body of the message with nothing strange in it.

begin 666 pakbon haven Ningbo.JPG
M_]C_X `02D9)1@`!`0$!+ $L``#_X0?P17AI9@``24DJ``@````'`!(!`P`!
M`````0```!H!!0`!````8@```!L!!0`!````:@```"@!`P`!`````@```#$!
M`@`4````<@```#(!`@`4````A@```&F'! `!````F@```,0````L`0```0``
M`"P!```!````061O8F4 at 4&AO=&]S:&]P(#<N, `R,# W.C$P.C Q(#$X.C$R
M.C(X``,``: #``$```#__P```J $``$````@`P```Z $``$```!+`@``````
M``8``P$#``$````&````&@$%``$````2`0``&P$%``$````:`0``* $#``$`
M```"`````0($``$````B`0```@($``$```#&!@```````$@````!````2 ``
M``$```#_V/_@`!!*1DE&``$"`0!(`$@``/_M``Q!9&]B95]#30`"_^X`#D%D
M;V)E`&2 `````?_;`(0`# @(" D(# D)#!$+"@L1%0\,# \5&!,3%1,3&!$,
M# P,# P1# P,# P,# P,# P,# P,# P,# P,# P,# P,# $-"PL-#@T0#@X0

This goes on a bit until we get this:

M6***`"BBB@`HHHH`****`"BBB@`HHHH`****`"BBB@`HHHH`****`"BBB@`H
MHHH`****`"BBB@`HHHH`****`"BBB@`HHHH`****`"BBB@`HHHH`****`"BB
MB@`HHHH`****`"BBB@`HHHH`****`"BBB@`HHHH`****`"BBB@`HHHH`****
M`"BBB@`IJEB6RN #A3D'<,#YN.G/:G44`%%%% !1110`4444`%%%% !1110`
I4444`%%%4M2ED at T^]FB8I+%:SR1N,':Z1LRL`05." <$$'H010!__]D`
`
end

-------------------------------------

Does anyone have any solutions for this very strange problem because
when I send this message to my own email-adres the client recognizes the
.JPG and shows it as an attachment but mailscanner doesn't.

Hope to hear from you soon.

Kind regards,
Wessel Kranenborg