(PHP3 >= 3.0.3, PHP4 )
imap_uid -- This function returns the UID for the given message sequence numberint imap_uid (int imap_stream, int msgno)
This function returns the UID for the given message sequence number. An UID is an unique identifier that will not change over time while a message sequence number may change whenever the content of the mailbox changes. This function is the inverse of imap_msgno().