Returns an array of message numbers sorted by the given parameters.
Reverse is 1 for reverse-sorting.
Criteria can be one (and only one) of the following:
SORTDATE - message Date
SORTARRIVAL - arrival date
SORTFROM - mailbox in first From address
SORTSUBJECT - message subject
SORTTO - mailbox in first To address
SORTCC - mailbox in first cc address
SORTSIZE - size of message in octets
The flags are a bitmask of one or more of the following:
SE_UID - Return UIDs instead of sequence numbers
SE_NOPREFETCH - Don't prefetch searched messages
Parameter charset was added in PHP 4.3.3.