In procedure acs_mail_body_to_output_format
line 400 (after: set content [lindex $contents 1]) add:
ns_set put $headers "Content-Type" "$content_type; charset=iso-8859-1"
ns_set put $headers "Content-Encoding" "8bit"
in procedure acs_mail_encode_content
line 336 (after: append content "--$boundary
") add:
append content "Content-Type: $c_type; charset=iso-8859-1
"
hope it helps