Unsupported operation :not writeable python

You open the variable "file" as a read only then attempt to write to it:

file = open('ValidEmails.txt','r')

Instead, use the 'w' flag.

file = open('ValidEmails.txt','w')
...
file.write(email)

file = open('ValidEmails.txt','wb')
file.write(email.encode('utf-8', 'ignore'))

This is solve your encode error also.