Hello Ansari,

This is due to the fact that setoolkit is run under Python 3, and several functions return strings rather than bytes. As a temporary workaround, you can use setoolkit with python2 to resolve the problem.

If you're using Kali, simply run (sudo python /usr/share/set/setoolkit).

It should also work. If you're using something different or setookit is installed somewhere else, simply locate the setoolkit application and run it with Python2.

If you want to learn a better way to spoof emails, I suggest you to visit the following article: https://medium.com/purple-team/social-engineering-and-possible-attack-vectors-ae6cecf4ced6