sortthread

// Assuming c is an IMAP client
var c *client.Client

// Create a new SORT client
sc := sortthread.NewSortClient(c)

// Check the server supports the extension
ok, err := sc.SupportSort()
if err != nil {
	log.Fatal(err)
} else if !ok {
	log.Fatal("Server doesn't support SORT")
}

// Send a SORT command: search for the first 10 messages, sort them by
// ascending sender and then by descending size
sortCriteria := []sortthread.SortCriterion{
	{Field: sortthread.SortFrom},
	{Field: sortthread.SortSize, Reverse: true},
}
searchCriteria := imap.NewSearchCriteria()
searchCriteria.SeqNum = new(imap.SeqSet)
searchCriteria.SeqNum.AddRange(1, 10)
uids, err := sc.UidSort(sortCriteria, searchCriteria)
if err != nil {
	log.Fatal(err)
}

log.Println(uids)

Output:

// Assuming c is an IMAP client
var c *client.Client

// Create a new THREAD client
sc := sortthread.NewThreadClient(c)

// Check the server supports the extension
ok, err := sc.SupportThread()
if err != nil {
	log.Fatal(err)
} else if !ok {
	log.Fatal("Server doesn't support THREAD")
}

layoutISO := "2006-01-02"
searchCriteria := imap.NewSearchCriteria()
date, _ := time.Parse(layoutISO, "2019-07-05")
searchCriteria.Since = date
threads, err := sc.UidThread(sortthread.References, searchCriteria)
if err != nil {
	log.Fatal(err)
}

log.Println(threads)

Output: