SMTP Excel corrupted attachment files

I've 开发者_开发知识库created a VB6 application from which I wish to send an SMTP email. The email is sent and received fine but when attaching an Excel 2003 file, whilst this is received okay, when trying to open it file becomes corrupt... I've also tried saving the attachment and then opening it but the problem persists. Thank you for any assistance...

The attachment data must be encoded. Not all mail servers and clients are 8-bit safe. Base64 is the most common encoding method.