nb mail unseen:
SELECT COUNT(*) FROM messages WHERE id_recipient = $id_member AND seen = 0 AND deleted_recipient = 0;
GET mail
SELECT * FROM messages WHERE id_recipient = $id_member AND deleted_recipient = 0;
GET mail sent
SELECT * FROM messages WHERE id_sender = $id_member AND deleted_sender = 0;
list del msg(ONLY received msg)
SELECT * FROM messages WHERE id_recipient = $id_member AND deleted_recipient = 1;
SET msg seen (WHEN recipient VIEW msg)
UPDATE messages SET seen = 1 WHERE id_msg = $id;
del msg recipient
UPDATE messages SET deleted_recipient = 1 WHERE id_msg = $id;
del msg sender
UPDATE messages SET deleted_sender = 1 WHERE id_msg = $id