Sometimes you might receive spam that looks like it's from a newsletter. This happens when a spammer includes an unsubscribe link in the email's headers.
It's not currently possible to use theMark as spam option to remove multiple emails containing an unsubscribe link in the email headers.
In this scenario, a bulk move can be performed by selecting all of the emails and then performing a drag and drop to place them in the spam folder. Alternatively, select the email and click More actions > Move > select "Spam" > Move.