Open message in modal or in separate page?

Unfortunately I can't provide visual examples now, I hope that's not a problem.

The question is simple: we have an inbox, which displays all the private messages a user has received, nothing new so far. When the user wants to open/read one of the messages, what should happen?

• Open the message in a modal(if so, where should it be positioned? On the side of the screen, or in the middle of it? It only counts on desktop though)
• Open it in a new page. Obviously for this we need to create a separate page for viewing single messages.

I also thought about maybe doing both, but I'm so not sure.

I know many say modal are a "no-go" in general, but let's put that aside for now.

I've been thinking about it probably for days, but I can't make up my mind, so I'd appreciate if you helped me out a bit.

In your experience, which one do you think would be a better way of doing it?