In order to add a gmail based email address please refer to the following easy to do step by step guide:
Here is the video for it:
3. Once the above steps are finished please feel free to add the address to the filtering under settings menu:

Here are the needed settings that you might copy/paste:
email address - your gmail address
password - app specific password
server for incoming email - imap.gmail.com
type - IMAP
port - 993
username - your email address
Please feel free to contact support if there are still questions left.
Keywords: gmail, google, OAuth2