`mail.outbox` not being set?

Hey there, thanks for pytest-django! Appreciate all of the hard work, have used it quite a few times with no problems.

We're running into a bit of a snag where we upgraded some things and suddenly mail.outbox isn't retaining emails during tests. I've tried to figure out how exactly to use the mailoutbox fixture as documented here but I am having trouble using this.

Right now we're testing in a class and I have tried quite a few configurations to pass mailoutbox fixture. I.e. I updated the ini:

[pytest]
usefixtures = mailoutbox

Not exactly sure how to use that fixture though, I tried adding the positional argument mailoutbox to my class methods, still not able to access it.. I am sure I am missing something simple.

Would appreciate a push in the right direction -- and again, thanks so much for this project!

Start with the mailoutbox fixture documentation linked in the issue and compare its usage with the class-based test methods and pytest.ini configuration described. Reproduce the reported behavior after the dependency upgrade, then determine whether the documented fixture usage works or whether the documentation needs clarification.