Domain key identified mail (DKIM) uses public and private keys to ‘sign’ an email you’re receiving. This often prevents messages from hitting spam or junk, and isn’t completely necessary. However, it’s worth adding DKIM verification to your email domain. Different providers have their own techniques for doing so, but once it’s up, send a test email to yourself and check the signature and authentication headers. When you rotate to another DKIM key, test again.