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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.