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.