AOL Whitelist

Also, to keep your AOL address book simpler, you can whitelist by manually managing your spam settings.

Click on “Spam Controls” in the lower right side of your inbox, and in the “Mail & Spam Controls” window that appears, click “Custom sender list,” and select “Allow email from.”
Input the email address you want to whitelist
Click “Save.”

With some reverse blacklisting, you whitelist a contact!

Gmail filter

Option 2: The message is from a trusted sender
If you know a sender is legitimate, you can remove the warning from their messages in the future.

Remove the warning from one sender at a time
On your computer, open Gmail.
Next to Search Search, click the Down arrow Down Arrow.
In the "From" field, type the sender's email address.
In the bottom right, click Create filter with this search.
Check Never send it to Spam.
Click Create filter.