Is Murena email optional or obligatory?

[obacht]

@buzzears

Removing the account under Account Settings,

That should be it.

@buzzears

Murena app

What app exactly? I do not have a “murena app” on my phone.
“Mail”-app ?
Thats a default app that comes with eOS and thus is not meant to be uninstalled.
Just do not use it and you are fine.
Or take a look here: Uninstall default apps - #29 by AnotherElk

@buzzears

but it comes up with a warning box that doing so might make the app misbehave.

Just give it a try as you obviously do not want to use it anyways - thus misbehaviour should not bother you … And you can just start the app again - in case it does.