You can have some Mail apps highlight (in red) email recipients with "outside" domains. https://support.apple.com/kb/PH19137?locale=en_US https://support.apple

You can have some Mail apps highlight (in red) email recipients with "outside" domains. https://support.apple.com/kb/PH19137?locale=en_US https://support.apple.com/kb/PH19137?locale=en_US https://arstechnica.com/civis/viewtopic.php?f=15&t=1299903 https://arstechnica.com/civis/viewtopic.php?f=15&t=1299903 (Outlook macro)