Server :: Smtp Proxy Filter To External Isp Smtp?

In order to have greater control over the emails sent out the company I imagined the following scenario.ScenarioDescribing in words what I need.ser sends an email to user@hotmail.com for example, using the smtp of my isp (is the internet).Before the email is sent, the firewall checks if the recipient is blocked transparent, if you are locked out rejects the email.I searched several forums and mailing lists, but did not find scenarios similar to mine.Where found situations in which the mail servers were internally in the company, which is not my case.