[exim] strange quoted-printable problem

Hello,

Recently I've run into a peculiar attachment problem. A client of mine is
receiving e-mail attachments from its customers. The attachments may 8-bit
with embedded JPEG images. Thus the beginning of the file is 8-bit text with
CR LF characters and the end binary.

Unfortunately some mailers (Windows based) appear to attach these as
quoted-printable. At some point during the mail transfer the binary 0D and
0A characters are rewritten into new line characters in the quoted-printable
data. This in turns results in corrupt JPEG data.

My customer is running Exim 3.35 but I have also managed to confirm this
behaviour with Exim 4.44.

My question is - does Exim (I'm also using Exim as an MDA) store mail
verbatim as received or is it possible the data gets mangled during SMTP?
Unfortunately I have very limited possibilities in looking into the sending
components.

Looking forward for any insight.


Dominique