http://www.sendmail.org/patchps.html

To provide protection for internal MTAs, 8.12.9 changes by default (char)0xff to (char)0x7f in headers etc.
To turn off this conversion compile with -DALLOW_255 or use the command line option -d82.101 when invoking sendmail.

To provide some protection for internal, unpatched MTAs that may be performing 7 to 8 or 8 to 7 bit MIME conversions, the default for MaxMimeHeaderLength has been changed to 2048.
Note: this does have a performance impact, and it only protects against frontal attacks from the outside. To disable the checks and return to the defaults that were active before these patches,
set MaxMimeHeaderLength to 0/0, i.e., in your mc file:

define(`confMAX_MIME_HEADER_LENGTH', `0/0');

Note: an MTA that is not patched might be vulnerable to data that it receives from untrusted sources, which includes DNS.

つまり、このバージョン8.12.9 から、添付ファイルの文字化けの可能性あり？ってこと？

sendmailの終焉か？