This tool validates if gmail addresses and corporate emails with google mail servers are valid without being authenticated. The default thread is 10 to avoid being rate limited.
python -m pip install gmailify
python -m gmailify -e example@gmail.com
python -m gmailify -f emails.txt
python -m gmailify -p http://127.0.0.1:8080 -f emails.txt
python -m gmailify -f emails.txt -o output.txt