Windows Live Mail ID Error: 0x800CCC6F. How can I solve it???

Hello... Can anyone help me???

I´m using Windows Live Mail a a recent error appears:

Error desconocido.

Asunto 'Estadistica Descriptiva - Proyecto modulo inv descriptiva - s1.pptx [01/16]'
Error de servidor: 554
Respuesta del servidor: 554 5.6.1 Messages of type message/partial are not supported
Servidor: 'pod51004.outlook.com'
Id. de error de Windows Live Mail: 0x800CCC6F
Protocolo: SMTP
Puerto: 587
Seguridad (SSL): Sí

And I have 17 messages unsent. How can resolve it, or at least, find the message to delete it...???

Thanks...