cannot receive but can send email

I can send but cannot receive email.

I can get my email via web mail but not on my iMac.

I can send and receive email on my Mac Pro laptop that uses the same router.

The problem seem to be in the iMac.

My service provider went through hoops trying to find the problem but concuded it is with my iMac

Need help to solve this.

Thanks to anyone who can help.