How can you tell if someone has seen your Facebook Message?

[Mark]

More than a year ago I sent a former teacher a message on Facebook who is not on my friends list, but it has always been on the 'sent' sign. Facebook definitely had the 'seen' feature back then.

But here are some questions I have: Does the 'seen' notification still work if someone isn't on your friends list and has read the message. Does the 'seen' notification still work if someone has read your message but then deleted it as soon as they read it?

Initially I thought that it had gone into the 'other' box but I have noticed that Facebook usually notifies you when a message goes into the other box. Could it be the case that the person I sent the message to simply deleted it and chose not to 'open' or 'read' it? Thanks a lot.

[abraXus]

facebook does not notify users when a message is sent to the "other" box - your teacher probably just never knew the message is there