Sensitive email-attachements (e.g. balances sheets or product data) should be encrypted with the PGP procedure before sending within the group and also to external business partners.
Basically all commercial and open-source PGP encrypting programs are compatible to each other. However it is recommended to use the software package WinPT because it proved itself well so far and in addition is free of charge.
You can include the public key of the persons listed above very simply in your "keyring" by right-clicking on the respective name and selecting "Save target as". As soon as you stored the zip-compressed .asc file on your Computer, you only have to double-click the file in your Windows Explorer. After that the key should be available in the mentioned above WinPT program, which of course has to be installed before.n Now you can send encrypted and highly secure eMails to the respective persons.