diff --git a/internal/tui/mail.go b/internal/tui/mail.go
index 6f553bbb..be989410 100644
--- a/internal/tui/mail.go
+++ b/internal/tui/mail.go
@@ -957,7 +957,7 @@ func (v *mailView) HelpBindings() []helpBinding {
 	if v.inThread {
 		bindings := []helpBinding{{"r", "reply"}, {"f", "forward"}}
 		if v.fileablePosting() != nil {
-			bindings = append(bindings, helpBinding{"l", "reply later"}, helpBinding{"a", "set aside"})
+			bindings = append(bindings, helpBinding{"l", "reply later"}, helpBinding{"a", "set aside"}, helpBinding{"t", "trash"})
 		}
 		if len(v.entries) > 1 {
 			bindings = append(bindings, helpBinding{"j/k", "next/previous message"})
@@ -1266,7 +1266,7 @@ func (v *mailView) HandleContentKey(msg tea.KeyPressMsg) tea.Cmd {
 			if v.topicID != 0 {
 				return v.loadForwardContext(v.topicID, v.topicName)
 			}
-		case "a", "A", "l":
+		case "a", "A", "l", "t", "T":
 			return v.fileOpenThread(msg.String())
 		case "[":
 			v.moveAttachmentCursor(-1)
@@ -2326,6 +2326,12 @@ func (v *mailView) fileOpenThread(key string) tea.Cmd {
 	if move == nil {
 		return nil
 	}
+	// Set Aside and Reply Later leave the thread on screen, in the box it landed
+	// in, so the next filing key can act on it there. Trash closes it: the Trash
+	// is not a box you file out of, and the web app returns to the list too.
+	if key == "t" || key == "T" {
+		v.ExitThread()
+	}
 	// Filing keys pressed faster than their requests answer can complete out of
 	// order, so each dispatch takes a sequence number and only the latest one
 	// records where the thread landed.
diff --git a/internal/tui/mail_test.go b/internal/tui/mail_test.go
index 27cb6956..b500a5c8 100644
--- a/internal/tui/mail_test.go
+++ b/internal/tui/mail_test.go
@@ -2409,6 +2409,120 @@ func TestMailViewContentKeyInThread(t *testing.T) {
 	v.HandleContentKey(keyPress("up"))
 }
 
+func TestMailViewTrashesTheOpenThreadAndReturnsToTheList(t *testing.T) {
+	for _, key := range []string{"t", "T"} {
+		t.Run(key, func(t *testing.T) {
+			v, recorded := mailWithTestServer(t, http.StatusNoContent)
+
+			v.Update(runCmd(v.HandleContentKey(keyPress("enter"))))
+			if !v.inThread || v.threadPosting.ID != 100 {
+				t.Fatalf("thread state = open:%v posting:%d", v.inThread, v.threadPosting.ID)
+			}
+
+			cmd := v.HandleContentKey(keyPress(key))
+			if v.inThread {
+				t.Error("trashing the open thread should return to the list")
+			}
+			done, ok := runCmd(cmd).(postingActionDoneMsg)
+			if !ok || done.err != nil {
+				t.Fatalf("trash command returned %#v", done)
+			}
+			if done.postingID != 100 || done.effect != postingActionRemove {
+				t.Errorf("action = posting %d effect %v, want posting 100 effect %v", done.postingID, done.effect, postingActionRemove)
+			}
+			if recorded.method != http.MethodPost || recorded.path != "/postings/trash.json" {
+				t.Errorf("request = %s %s, want POST /postings/trash.json", recorded.method, recorded.path)
+			}
+			if len(recorded.body.PostingIDs) != 1 || recorded.body.PostingIDs[0] != 100 {
+				t.Errorf("posting_ids = %v, want [100]", recorded.body.PostingIDs)
+			}
+
+			answer, _ := v.Update(done)
+			if toast := deliverToView(v, answer); toast != "Thread moved to Trash" {
+				t.Errorf("toast = %q, want %q", toast, "Thread moved to Trash")
+			}
+			if len(v.postingList.postings) != 1 || v.postingList.postings[0].ID != 101 {
+				t.Errorf("postings after trashing = %v, want the other thread alone", v.postingList.postings)
+			}
+		})
+	}
+}
+
+// Trash keeps to the same rule as the other filing keys: a thread opened over
+// search results or a bundle has no row to file, so the key says so rather than
+// trashing whatever the box list's cursor happens to be sitting on.
+func TestMailViewRefusesToTrashAThreadOpenedFromSearchResults(t *testing.T) {
+	v, recorded := mailWithTestServer(t, http.StatusNoContent)
+	v.searchActive = true
+	v.searchQuery = "quarterly planning"
+	v.searchList.setPostings([]mail.Posting{{ID: 10, TopicID: 100, Name: "Hello world"}})
+
+	v.Update(runCmd(v.HandleContentKey(keyPress("enter"))))
+	if !v.inThread {
+		t.Fatal("the searched thread should have opened")
+	}
+
+	if cmd := v.HandleContentKey(keyPress("t")); cmd != nil {
+		t.Errorf("trash over search results returned %#v, want nothing", runCmd(cmd))
+	}
+	if !v.inThread {
+		t.Error("a refused trash should leave the thread open")
+	}
+	if v.notice == "" {
+		t.Error("a refused trash should say why")
+	}
+	if recorded.path == "/postings/trash.json" {
+		t.Error("a refused trash still asked the server to trash something")
+	}
+}
+
+func TestMailViewCannotTrashAThreadOpenedWithoutItsPosting(t *testing.T) {
+	v, recorded := mailWithTestServer(t, http.StatusNoContent)
+	v.Update(topicLoadedMsg{
+		topicID: 100,
+		title:   "Hello world",
+		entries: []mail.Entry{{Creator: mail.Contact{Name: "Alice"}, Body: htmlutil.ToMarkdown("<p>hello</p>")}},
+	})
+
+	if cmd := v.HandleContentKey(keyPress("t")); cmd != nil {
+		t.Errorf("trash without a posting returned %#v, want nothing", runCmd(cmd))
+	}
+	if !v.inThread {
+		t.Error("a refused trash should leave the thread open")
+	}
+	if v.notice == "" {
+		t.Error("a refused trash should say why")
+	}
+	if recorded.method != "" {
+		t.Errorf("a refused trash sent %s %s", recorded.method, recorded.path)
+	}
+}
+
+func TestMailViewTrashesAThreadOpenedFromPreviouslySeen(t *testing.T) {
+	v, _ := mailWithTestServer(t, http.StatusNoContent)
+	loaded, _ := runCmd(v.handleBoxShortcut("9")).(seenLoadedMsg)
+	v.Update(loaded)
+	v.Update(runCmd(v.HandleContentKey(keyPress("enter"))))
+	if !v.inThread || !v.seenActive || v.threadPosting.ID != 611 {
+		t.Fatalf("thread state = open:%v seen:%v posting:%d", v.inThread, v.seenActive, v.threadPosting.ID)
+	}
+
+	done, ok := runCmd(v.HandleContentKey(keyPress("t"))).(postingActionDoneMsg)
+	if !ok || done.err != nil || !done.seen {
+		t.Fatalf("trash command returned %#v", done)
+	}
+	if v.inThread || !v.seenActive {
+		t.Errorf("trashing landed on open:%v seen:%v, want the Previously Seen list", v.inThread, v.seenActive)
+	}
+	v.Update(done)
+	if len(v.seenList.postings) != 0 {
+		t.Errorf("seen postings after trashing = %+v, want the row gone", v.seenList.postings)
+	}
+	if len(v.postingList.postings) != 2 {
+		t.Errorf("a seen-screen trash landed on the box list: %+v", v.postingList.postings)
+	}
+}
+
 // --- Subnav ---
 
 func TestMailViewSubnavItems(t *testing.T) {
@@ -3080,6 +3194,19 @@ func TestMailViewHelpBindings(t *testing.T) {
 	}
 }
 
+func TestMailViewOpenThreadHelpOffersTrashOnlyWithAPosting(t *testing.T) {
+	v, _ := mailWithTestServer(t, http.StatusNoContent)
+	v.Update(runCmd(v.HandleContentKey(keyPress("enter"))))
+	if !hasHelpBinding(v.HelpBindings(), "t") {
+		t.Errorf("help bindings = %v, want trash among them", v.HelpBindings())
+	}
+
+	v.threadPosting = mail.Posting{}
+	if hasHelpBinding(v.HelpBindings(), "t") {
+		t.Errorf("help bindings = %v, want no trash without a posting", v.HelpBindings())
+	}
+}
+
 // A label scrolls rather than paging, so it advertises no page keys and p keeps meaning
 // paper trail.
 func TestMailViewLabelHelpOffersNoPageKeys(t *testing.T) {