Here is the problem : customer has 2 SMTP servers, one used for internal emails and one used for external emails.
Currently, with SSPR 4.5, you can only configure one SMTP server (well, technically, you can configure an additional SMTP server, but that's only for fault tolerance. The additional SMPT server is used in case the first SMTP server is not responding).
The idea would be to allow SSPR to be configured with multiple SMTP servers, and to define criteria based on the email address to specify which SMTP server to be used. For example, it could be something like this :
➜ All emails addresses containing the domain "@mycompany.com" would go to the first SMTP server
➜ All other emails addresses would go to the second SMTP server