Mail app not working suddenly. Stuck on checking for mail

Hi,

My mail app using yahoo mail has always worked fine.

It has suddenly got stuck on "checking for mail" on all mailboxes and won't send emails.

It receives emails but not the content of the message and also won't load older messages from server.

I am on wi-fi at home, the same as I always have used and other internet/data apps work.

I need this to work more than imessage as use email on phone frequently.

Please does anyone have any advice at all?

Would be greatly appreciated!

This is on iphone 3gs 8gb ios 6 .1.6