MacWorld – Autocompleting addresses and address suggestions are powerful shortcuts that can easily bite you. You are likely not planning a military action in another country, but the accidental inclusion of unintended invitees to a group text, email, or other discussion could still prove a problem—from embarrassment to losing friends, causing a family rift, or even being fired from a job. The problem arises from two intersecting factors: how Apple and third-party software retain recipients’ information to make it easy to use in future messaging, and how quickly apps have trained us to type a few letters and move on without examining what’s being autocompleted and filled in. This means that you might intend to add “Jeffrey Pixenwald” to a group chat and instead invite “Jenny Hickenlooper” by typing “Je.” It happens. A great general place to start when inadvertently selecting the wrong person is your Contacts list. This list may contain people you’ve only connected with once years ago. Delete unwanted entries. You can also clear out the macOS Mail app’s list of suggestions, which I explain below in the Mail section.More generally, consider the following:

• Slow down when selecting contacts from autocomplete suggestions to ensure you read what’s suggested.
• Always double-check recipients before sending a message or email.
• Type the full name for important or sensitive messages rather than relying on autocomplete. This avoids any accidental overlap, even though it’s tedious.

Here is more app-specific advice on how to avoid autocomplete filling in the names, phone numbers, and email addresses of people you didn’t intend to include in your communications…”