My attempt to block an unwanted e-mail has failed by using outlooks ‘block a sender’

I am receiving unwanted e-mails in my junk box. I have used Outlooks block a sender or domain server yet the e-mail continue. The are from the following senders: Canadian **** Online **** and Viagra Online, all use different e-mail address. They change their e-mail address often too. I want to block their 'domain sever' to stop them from sending me e-mails to my junk box ! I have check the 'source' of the e-mail and found their 'return e-mail' address their. still they cannot be stopped ! Any ideas ?