Microsft Sharepoint e-mail failure

We have set-up a Sharepoint server and everything is working fine. The problem we are facing is that tasks, workflows are unable to send e-mails to the target recipient but is able to send e-mail to the originator say of a workflow.

Could someone out the be having a solution so that we get the e-mails to be sent to the recipient who could be say approvers within workflows.

David