- Facebook does not store your deleted messages once you have selected them to be deleted.
It can take a few moments to a few days for the server to cycle; however, most companies such as Facebook are not willing to go into the deleted files to recover the data or see if the data can be recovered.
Basically, once you have deleted a message it will be gone forever. It happens as quickly as possible so as to make space for new messages. The size of Facebook's following means it is important that their system is continually refreshed by removing the old information so that new information can be stored. This is why once a message is deleted it will be gone within the next login.
There is a way to test the server, but this isn't a permanent solution. Sometimes you can hit the back button on your web browser and find your deleted messages are still there. However, this only works if you pressed the back button within seconds and you did not log out. This is because the back button only returns you to a page memory so the message will permanently disappear once you do log out.
You may find that, even after a few seconds, pressing the back button won't bring the message back; this just depends on how quickly things work for the day. It is best to be absolutely sure you want to delete a message before you do so.