Email tracking?

I think it was spam.
They write you one time, and, if you reply, you give them confirmation your e-mail account is active, so they can actively spam you.

Thats what they wanted for you to reply so they know its a real address

I would recommend never replying to an email unless you know the sender. Your just asking for a SPAM sandwich.

Never reply to spam. There’s nothing you can possibly gain by doing so. There’s zero way of finding out who sent an email, let alone through a free email service provider. You can Google the email address to see if it comes up elsewhere and that could provide you with hints to who it is (if it’s an actual person), but if it’s spam, there’s no way of finding out, and there’s also no point in trying.

Now they know you have a valid and active account, you’ll probably see more weird emails in the future.

Greeeeat.

gmail
settings

find the setting similar to “require approval for external content”

no more tracking