$ echo  "john.doe@gmail.com" | sed 's/"([^"]*)"//g'
john.doe@gmail.com

$ cat ~/Desktop/emails.txt
"john.doe@gmail.com"
$ sed 's/"([^"]*)"//g' ~/Desktop/emails.txt
"john.doe@gmail.com"
$ sed -i '' 's/"([^"]*)"//g' ~/Desktop/emails.txt
$ cat ~/Desktop/emails.txt
"john.doe@gmail.com"