imap_uid
(PHP 3>= 3.0.3, PHP 4 )
imap_uid -- This function returns the UID for the given message sequence numberDescription
int imap_uid ( resource 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().
Note: This is not supported by POP3 mailboxes.