php man page for imap_uid

IMAP_UID(3)								 1							       IMAP_UID(3)

imap_uid - This function returns the UID for the given message sequence number

SYNOPSIS
       int imap_uid (resource  $imap_stream, int  $msg_number)

DESCRIPTION
	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(3).

PARAMETERS
	      o $
		imap_stream -An IMAP stream returned by imap_open(3).

	      o $msg_number
		- The message number.

RETURN VALUES
	The UID of the given message.

NOTES
       Note

	       This function is not supported by POP3 mailboxes.

SEE ALSO
       imap_msgno(3).

PHP Documentation Group 													       IMAP_UID(3)