If you have 2-Step Verification enabled and you want to use a password,  you need to generate an Application-specific password for MailtoX Desktop or MailExplorer. 

1. Go to your
Google Account Settings Page and select “Security“.

2. Under the “Signing in to Google” section click on ”
App passwords.”

3. You will get a page where you can generate the password. Under the “Select App” drop-down select ”

4. Under the “Select Device” dropdown, select “Windows Computer”

5. Click on Generate to obtain the password

You can use the generated password to login to Gmail

You can learn more about Gmail 2-Step verification at: