What is white check mark on messenger?

The white check mark on messenger indicates that your message has been sent successfully to the recipient's device. It does not indicate whether the recipient has seen or read your message. If the check mark turns into a filled-in blue circle, it means that the recipient has received and seen your message. If there are two blue check marks, it means that the recipient has received and read your message. However, if the recipient has turned off read receipts, you will not see the filled-in blue circle or the two blue check marks.