Test passwords and e-mail on other sites?

I would like to know whether it is legal to test e.g. Email and password from a Minecraft account with PayPal or Google and with other providers

You can try usernames and passwords on Google and GMX until you go black, of course.

It becomes illegal if you mess around with the data or external accounts or even commit criminal offenses.

Thank you.

If it's your own data, you can do that. If it is foreign data, probably not.

OK