[perardi]

Extremely anecdotally: it’s [person_name]@gmail.com

I know of very few friends who go through the process of creating a burner email account to sign up for Grindr. Now, maybe that’s different in other countries, but at least in the States, I would bet good money you can guess their Gmail address.

[johnday]

In the case of gmail accounts you could simply prepend +grindr or any other name to the user part of the email address to get something (relatively) unguessable.

[jdminhbg]

You could do that, but most users don't.