Computer Help and Support

Hotmail is an email provider, yahoo is also, so is gmail. Email providers generally adhere to the same protocols (POP3/SMTP) which means any email client (what you're calling an app) that works with one can work with another (though it can be the case that it's 'pay' based like you have to 'upgrade' your account w/yahoo to get them allow you to access your other email accounts, just as a for instance).

I access my Yahoo Email account through the Microsoft Mail app on my Windows 10 machine. There's nothing inherently proprietary about how email works