I set up a filter for myself, but I strongly encourage you to set a spam filter for:

*@*.firebaseapp.com

The amount of spam in my Dynu spam box is totally ridiculous. They have been inundating me for months. The change the lower level domain on a constant basis. I set the spam filter to:

firebaseapp.com

They attempt to send me several hundred spam emails/month.

I assume other users here have the same. If at the Dynu domain level you could save a LOT of resources.