Sensitive Information
The best and safest way to transfer sensitive information (such as a credit card number) will always be through a direct phone conversation.
However, there may be some instances where you are dealing with an overseas customer or individual, and a phone call would not be possible. If this is the case, there are still ways to get the necessary information to the recipient, albeit not as safe and secure as a one-on-one phone call.
Access Control Link
In Windows Explorer (press WIN+E), you can share ANYTHING on your PC, whether it's on your personal company OneDrive or not.
In this example, we're using a OneDrive synced folder.
After clicking Share, you can input the users who you would like to share this document. You can also click on the Gear icon to edit additional settings, such as adding a password / expiration date / permission.
If you set a password, the best way to inform the recipient of that password would, again, be through a phone conversation. But that can be sent in an additional follow-up email through Outlook's encrypted option.
If for whatever reason OneDrive is not available to you (which in nearly every case it should be), you can also password protect a Microsoft Word document and send it attached via an Outlook encrypted email. It is recommended to only include partial information in this document, and then send the rest in a follow-up email as well as the password to the original document.
You can password protect a Microsoft Word document by clicking File (top left corner) > Info > Protect Document > Encrypt with Password:
As mentioned originally, a phone conversation will always be the most secure way of transferring sensitive information. However, if that is not available, using a password protected / expiring OneDrive link, and sharing that password via an Outlook encrypted email will be the next best thing.