Q: how to block sender in mail

Stop unsubscribing to them. The spammers know immediately that they have a valid email address once you respond to them. They then sell/share your valid email address with other spammers. Legitimate companies may follow your unsubscribe instuctions but spammers certainly will not. Teach your email client which emails are spam by identifying the spam emails. Over time the email client will learn which emails are spam.

You don't say which email client you are using so I'll provide some links that may help:

iCloud: Identifying and filtering junk mail - Apple Support

http://www.macworld.com/article/2033767/dealing-with-junk-mail.html