(3.0.3 - 3.0.18 only, PHP 4 >= 4.0.0)
imap_uid -- This function returns the UID for the given message sequence numberThis 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().
Note: This is not supported by POP3 mailboxes.