Convert unencrypted connection to STARTTLS

Convert the unencrypted connection to STARTTLS. I - Our Problem: We have old ticket management software that can only communicate with unencrypted SMTP. This software has always connected with an Exim server without any problems. Now this software needs to connect our ticket management software to a Microsoft SMTP server that requires STARTTLS. II - Project requirements: 1) We need to intercept the unencrypted connection sent by the ticket management software and send the same connection with STARTTLS to Microsoft SMTP. 2) This connection converter (unencrypted for STARTTLS) must be created in a test instance that we will provide on [login to view URL] with CENTOS 7. This test instance (test environment) is not the same instance where it runs the ticket management software (production environment). 3) To test this project we are going to use Thunder Bird and configure SMTP pointing to the test server without encryption. Then the test server should redirect the connection to the target server with STARTTLS (Microsoft) and the emails should be sent correctly. That is all. If you are a Linux expert, this will be a quick and simple project for you.