use papercut
https://papercut.codeplex.com/
follow the article https://prasadpathak.wordpress.com/2014/10/31/sharepoint-using-papercut-for-testing-the-email-functionality-in-sharepoint/
Make sure the local SMTP server is created and configured and started from IIS 6.0
Disable the Simple Mail Server … service in Services
Set papercut to listen on port 25 local server