Why when i log into my hotmail, my messenger will automatic show appear offline to ppl?

I would like to ask why when i log into my hotmail to check my email, then my messenger will show appear offline to my friends?

Or when i log into my messenger, then when mail send in, i click to view my email, then my messenger will turn to appear offline to my contacts.

Can help me to solve my problem? Very headache of it.

Regards,

Jasic