If you have an email ending in @hotmail.com, @live.com or @outlook.com (or any other Microsoft-related domain), please consider changing it to another email provider; Microsoft decided to instantly block the server's IP, so emails can't be sent to these addresses.
If you use an @yahoo.com email or any related Yahoo services, they have blocked us also due to "user complaints"
The Seen Blocker for Facebook Messenger
Apparently, there is a need to block people from knowing you saw their messages.
Apparently, people want to not be caught reading a message so they can politely ignore it or pretend they didn't see it, so they install the Facebook Unseen add-on. I think its weird as hell. Like, why go through the trouble of ghosting somebody with an app? Why not just do it IRL? Like, giving them a potassium reply?