Nokia E90! Email sent from phone arrives asap but email sent to email on phone takes at least 10 mins to hours?

Why is this and can i do anything to speed it up? It is a yahoo email set up on the nokia messaging app which i downloaded from the nokia website. Email arrives asap online in the yahoo email box so whats the delay in arriving on the phone? iPhone email sending & recieving is asap. Also any other E90 pointers would be very welcome.