I put my website online yesterday and registered it with Google at the same time. Before that, I didn't even put a single link to the site anywhere online. And I don't have any email address on my site, just a mail form that is protected with ReCaptcha v. 2; see https://www.020webdesign.nl/bedrijfsinfo.php.
Still, I got a spam mail within 24 hours. :-((
I can tell that the mail was sent through the mail form, there's no doubt about that. It seems to have been entered into the form manually (even though I'm not sure about that), but how is it possible that the spammer found my site so quickly?