Q: Should Mac owners Purchase Anti Spam Software

Who is your email provider? Most have spam filters that can be set up on the server via their web-mail interface.

Have a look at SpamSieve - it's a plugin for Mail and other email clients and after a training period is very good at identifying spam and shunting it to a special folder from which you can check and delete it at your leisure. It's also configurable so you can specify parameters. It works with both POP and IMAP mail.

Please read if you have not already:

Mail (Yosemite): Reduce junk mail in your inbox