Send and Stock Emails in different Servers

Hi, We have many customer servers in external Data Centers, but our Official websites are hosted in our Local Web Server. Problem : All its okay, except Sending Emails from our Local Web Server are not delivered because our ISP don't want to set PTR (Reverse DNS) for our Public Static IP, so our Emails marked as Spam by Gmail, Yahoo, Hotmail.. . Solution : is possible to Stock Emails Data in our Local Web/Email Server, but Sending Emails from external IMAP Server ? Thank you,