They're probably being sent with a fake from header to make them look like you sent them to yourself. Pretty common with spam. Plesk's email system doesn't have a good spam filter, so you're likely going to receive most if not all spam sent to your domain. Decent spam filters will discard these fake From emails as sender spoofing.
That said, DKIM, SPF, and DMARC have been set up for the domain bochard.net. We recommend sending a real email (not just the word "test" or a blank email) to https://www.mail-tester.com/ to make sure that everything is set up correctly. If you get less than a 10/10 score please post a link to the full report so we can help you fix any other issues that there may be.