I got this error message since sending an email to an incorrect address and having it returned as undeliverable. I was trying to contact someone at my daughter's middle school and was unsure of a hyphenation in the address. The account is {removed email address}
Please unblock my account!
An unknown error has occurred. Subject '', Account: 'MrP3T3', Server: 'smtp.live.com', Protocol: SMTP, Server Response: '550 5.3.4 Requested action not taken; This account is currently blocked from sending messages. If you don't think you've violated the Windows Live Terms of Use, please contact customer support.', Port: 587, Secure(SSL): Yes, Server Error: 550, Error Number: 0x800CCC69