Best to mark such mail as Phishing, or junk or just block them.
If you use Gmail, you don’t need this “StartMail” he is pushing. You can create aliases right in Gmail. I have one for all the sites that require you to create a login and I don’t want their constant emails.
Gmail has an “Unsubscribe” button right next to any business email address, so you don’t need to click a suspicious link within the email to unsubscribe.
Before you click on a link in an email, you can hover over it and the address appears in the bottom left of your window. If it looks suspicious, don’t click on it!!
And of course, Gmail has the “Spam” button if you want to block them.