Windows Live Mail 0x800CCC0F

When using an Office 365 mailbox via IMAP with Windows Live Mail, sending messages may present a 0x800CCC0F error. Using the account in Thunderbird may also present timeout errors.

One reason for this is the system has IPv6 enabled, and your router and ISP enable IPv6.

Disable IPv6 on the network adaptor (or at the router, depending on what is suitable for your environment), which forces all requests to Office 365 over IPv4.