BuddyPress.org

one thread has one to many messages

one message has one to many recipients

one user has zero to many threads

the squiggly stuff you posted is a serialized array of message and sender ID’s. In PHP if you take that value and use the function unserialize() (or maybe_unserialize() if you are in the WordPress environment) you will get an array full of ID’s you can then iterate and use.