IMAP4.thread(threading_algorithm, charset, search_criterion[, ...])
The thread command is a variant of search with threading semantics for the results. Returned data contains a space separated list of thread members.
Thread members consist of zero or more messages numbers, delimited by spaces, indicating successive parent and child.
Thread has two arguments before the search_criterion argument(s); a threading_algorithm, and the searching charset. Note that unlike search, the searching charse