Hi. I just received an e-mail from a user who is harassed by thank spam. The user suggested that an option is added (in the thank recipient's Preferences) to require the thank sender to be in a user group (for example, autoconfirmed) for the thank recipient to see the notification. Currently, the options under Preferences → Notifications only offer the choice of allowing or disallowing thanks from everyone, which is a bit of a sledgehammer option.