cannot view bcc field in compose message

Open mail application > take cursor on view > if you check mark Cc Address field and Bcc Address field , and you compose a new mail ( command + N ) , both field will be shown , if you uncheck the mark in the desired field ( by clicking once again on the checkmark ) it will be not shown in compose window .You can select the desired field and click on it a right check mark will be saved in the field , you can select one field or either both ( according to your choice ) .

Was it your goal to always have the cc: and bcc: header fields default to present in every composed email, without your intervention, and whether you use these fields or not? There is a Bcc self in the Mail Preferences : General panel that is off by default.

On macOS Sierra 10.12.5, and Mail 10.3, I have dragged/dropped the Header Fields icon, from the customization panel to the toolbar, and this allows me an on-demand insertion of the appropriate bcc, cc, etc fields into the compose header. Once these are set, they automatically reappear for me in subsequent fresh launches of Mail and the compose window.

Why the Header Fields icon is not working for you when it does for me is the question.

The mail app is not showing the results , an assumption corruption .

If you are using IMAP account , open mail and its preferences > select Accounts delete the webmail account , add the account once again all mails will start downloading .

Do you use any Anti - Virus , cleaners , apps in your computer , as these cause corruption in applications .

In my opinion they must be uninstalled .

I once read that the use of bcc was against the law in France. Has the UK gone to that extreme yet? 😉