Properly storing an E-mail Password
I'm unsure about the proper steps to store the e-mail password on the user's computer.


There are two ways I would recommend (in tandem if possible).

First, some SMTP servers (like Google) allow you to create an Application Password.  This password has limited access (for instance just for email) and can't be used to change the users password.  

Secondly, use .Net's built in capability to encrypt the web.config/app.config.  The nice part here is that the configuration sections can just be read by your application, it doesn't know they are encrypted or not, .Net takes care of it for you.


  This may have been a bit unclear from the above, but I want to allow some person, for which I set up an Outlook account, to send mails to other persons


If the application is sending an email from the computer Outlook is installed on, you may want to consider How to open Outlook new mail window.