I registered a .as domain for my last name (ending in 'as') and managed to set it as my primary email on Facebook shorty before they decided to block that domain for no apparent reason. For years (until I deleted my FB account), I had a message on the top of my feed asking me to confirm my email even though it was already confirmed but I could never do it because of the block. Tried many times to get it resolved but no success. And to this day, people cannot send posts or messages that contain my domain (website or email) anywhere on Facebook and Instagram.