in reply to
Re^7: SMTP auth() command not supported on smtp.live.com
in thread SMTP auth() command not supported on smtp.live.com
I would try with a mail sender and recipient that are not hotmail, and I would also try sending a plain text attachment.
If sending a plain text attachment works, then it is a problem with binmode not being applied, somewhere along the chain.
If the problem goes away by not using Hotmail as the first SMTP server, or goes away by using a different recipient than Hotmail, then the problem is how Hotmail handles (this kind of) attachments.