Unlike when an email address is spoofed and proper email validation methods can be used, display name spoofing can be hard to identify. Often email client software only shows the display name and doesn't show the sending address. This can be dangerous when employees see a request come in from a name they recognize if they don't notice that the address isn't correct.
Often this type of attack is used to impersonate higher level management in a company. The following solution only works if you don't need mail from anyone that shares the name with the person being impersonated. You should be warned that using regex (regular expressions) can block messages you don't intend them to if the pattern isn't set up correctly or if the email in question isn't formatted as expected.