When you're sending sensitive information via email, it's best to do so with end-to-end encryption. Even better, set the email to destroy itself after a set amount of time for a little piece of mind.
It can be hard to get all of your friends, family, coworkers, and acquaintances to jump on board with the more-secure email system ProtonMail, but that doesn't mean you can't still send them encrypted emails. Best of all, they won't even have to install any other apps or extensions to read or reply to the messages.
Your display name in ProtonMail is what email recipients will see when they first receive your message in ProtonMail, Gmail, or another email provider. You can choose this name when you first set up your ProtonMail account, but it can also be set up after the fact if you skipped that step.