Be careful with email auto-complete. This is an email feature that automatically completes a name for you when you begin typing it in the TO field. However, your email client can easily complete the wrong name for you. If you are emailing anything sensitive, always be sure to check the TO field a second time before hitting the send button.
To learn more, check out this OUCH! newsletter: https://securingthehuman.sans.org/newsletters/ouch/issues/OUCH-201609_en.pdf
More cybersecurity education available here: https://www.youtube.com/playlist?list=PLQNZaWpmI1TfMOQMJ-ra1VSGgkuOPtFlA