To ensure you can easily verify a sender is the actual sender of an Email in Apple Mail (macOS only) you can choose to always show the sender’s email address.

To enable this do the following:

Open Mail > Preferences > Viewing > untick “Use Smart Addresses” checkbox.

If it is unchecked already and sender’s email addresses are not showing, then do the following:

1. check the box, close preferences, close Apple Mail.
2. next open Apple Mail > Preferences > Viewing > untick “Use Smart Addresses”
3. next close preferences, close Apple Mail
4. open Apple Mail once more and sender’s email address will show.