Very secure information can shared via email by using PGP. This writer has found the best application of PGP for Windows is with GPG4Win and it is very well integrated,via the right-click dialogue, to easily apply in the sharing of attached encryted files or folders. The application can be downloaded at the site for free (choose $0) if one doesn't wish to make a donation.
With the application installed, one first will require to establish a certificate (key-pair). Here are the steps required leading to an encrypted file or folder.
Creating a Certificate
Select the icon for creating a new certificate (a key-pair) by entering your name and email address. Remember to backup your certificate and place it in a secure folder. It will enable one to restore your key-pair.
Share the Public Key
Your public key can be thought of as a padlock. In sharing it with others, they can use your 'padlock' - your public key - to encrypt files/folders that they wish to send to you.
Encrypt a File/Folder By right-clicking on a file or folder, select Sign and Encrypt. The dialogue will set the file/folder to be encrypted with your certificate as well as an option to choose the public key of the targeted recipient(s). There after, the encrypted file is sent by any means to the recipient(s)
1. The first time using a new public key, The application 'Kleopatra' will open and one will be asked to 'certify' it. Simply click on the document link to complete the verification process. Thereafter, that particular public key will not invoke this dialogue.
2. One also has the option, in the choices to encrypt, to encrypt simply with a password by which anyone with that password can open it. Unlike the zipped folder (eg. such as with 7z ), this encypted file can be sent directly in an email message.