E-mails not posting

I’m a novice – I help maintain our website but I’m not familiar with much else, so I didn’t set up this plugin, however, the folks trying to use it have let me know it’s not posting. When I did a manual check to see why the posts weren’t going through, I got the following error code:

getemails: The username and password provided were not accepted for the IMAP server imap.gmail.com on port 993. A0002 NO [ALERT] Please log in via your web browser: https://support.google.com/mail/accounts/answer/78754 (Failure)

The page I need help with: [log in to see the link]