I asked what you were trying to do (as in use-case) so that I could try and point you in the right direction. There are a number of e-mail service integrations for some typical publishing needs - https://docs.ghost.org/integrations/email/?no-cache=1.
However, it seems to be that you’re under the impression Ghost is a development framework? The mailing configuration is so that Ghost can send invite e-mails when you invite users to your publication, nothing more. If you need to send e-mail from your own applications then you should use the library or service that best serves your needs.