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.