Trusted Senders are automatically added in two ways:
Automatically added Trusted Senders represent our guesses about mail you would always like to receive. If you have already released one message from a person, you would probably also like to receive their future messages. If you send mail to someone, you would probably like to receive their response.
On that page, click on the button that says
After clicking on that button, a few more options will appear.
If you want to whitelist an address (email@example.com) or a domain, (example.com), then under the Type drop-down menu, select "Address/Domain".
Next, type in the email address or domain that you are trying to add in the Email Address field.
You can also type in a name which will help you identify the trusted sender in a future scenario.
You can also whitelist Servers or Networks. Just change the Address/Domain drop-down to Server/Network and add the appropriate address.
Have a list of people you'd like to add as Trusted Senders? You can also upload a list of Trusted Senders for importing. Your file should either be a .txt file (email addresses only) or a .csv file (if you'd like to upload names and email addresses.)