How to "sendmail" with xls attachment , without using uuencode?

Hi ,
I have a script that uses sendmail , it has some html tags for the body, hence i am using sendmail.
Script works fine with uuencode , however i found that production environment doesnt support uuencode.

i tried openssl base64 < xlsfile.xls , the file is corrupted in mail , could you please suggest alternative.

echo 'content-type: application/vnd.ms-excel;name="'$(basename $input_file_name)'"'
echo "content-transfer-encoding: base64"
echo 'content-disposition:attachment;filename="'$(basename $input_file_name)'"'
openssl base64 < $input_file_name