imap_uid --
This function returns the UID for the given message sequence
number
Description
int imap_uid ( resource imap_stream, int msgno )
This function returns the UID for the given message sequence
number. An UID is a 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().
Замечание:
This is not supported by POP3 mailboxes.