You never want to accidentally send emails to users from your local or staging version of your site, especially if you run an e-commerce site with a bunch of customer data.
Fortunately it’s pretty easy to change all of the emails addresses in your users table to something with a fake domain by running this MySQL query:
update wp_users set user_email = concat(substring_index(user_email, '@', 1), FLOOR(rand() * 90000 + 10000), '@localhost.dev')
This will update the email domains to @localhost.dev and adds a random 5 digit number in case you have multiple email addresses with the same first part before the @.
You can repeat for any other columns in your database that might have email addresses, such as this one for Easy Digital Downloads:
update wp_edd_customers set email = concat(substring_index(email, '@', 1), FLOOR(rand() * 90000 + 10000), '@localhost.dev')
In addition you can run your WordPress email through something like Mailhog using a plugin. I don’t just recommend that because of the name 🙂