Error when i try to send an email

Every time i try to send an email i get this arror which says: cannot connect for an unknown reason. But before that it tryes to conect to 3G, but anyway i know there is some trubbles with my 3G but thats not the problem (dont ceare about 3G so i just dable it to get more baterytime). The thing is that i'm conected to internet trought wi-fi. But it seams that a lot of programs wont use it? Why? and how can i change this?