Can’t send email with smtp-mail.outlook.com, Server Response: 530 5.7.0 Must issue a STARTTLS command first

I can't send emails in Windows Live Mail.  Here is the error message I get:

The message could not be sent because the server rejected the sender's email address. The sender's email address was *** Email address is removed for privacy ***'.

Subject 'Re: Yugen'
Server Error: 530
Server Response: 530 5.7.0 Must issue a STARTTLS command first
Server: 'smtp-mail.outlook.com'
Windows Live Mail Error ID: 0x800CCC78
Protocol: SMTP
Port: 587
Secure(SSL): No

What is a STARTTLS command? 

Thanks for any help I can get.

***The post was moved to the appropriate forum category and personal information was deleted by the moderator. Please see the Microsoft Community Frequently Asked Questions for information on how you can protect your privacy.***

[Original subject: Can't send email in windows live mail]