diff --git a/web/src/views/compose/Composer.tsx b/web/src/views/compose/Composer.tsx
index b992f5f..99be5e5 100644
--- a/web/src/views/compose/Composer.tsx
+++ b/web/src/views/compose/Composer.tsx
@@ -38,6 +38,11 @@ export function Composer({ draft }: { draft: Draft }) {
   const [showToolbar, setShowToolbar] = useState(true);
   const d = draft;
   const key = d.key;
+  // Where the caret starts, decided once when the composer opens: a blank
+  // message starts in the recipients, a reply (already addressed and titled)
+  // starts in the body. Deriving this from live state would move the caret
+  // while the user types.
+  const [initialFocus] = useState(() => initialFocusTarget(draft));
 
   const patch = useCallback((p: Partial<Draft>) => update(key, p), [update, key]);
   const onHtml = useCallback((html: string) => update(key, { html }), [update, key]);
@@ -138,7 +143,7 @@ export function Composer({ draft }: { draft: Draft }) {
           )}
           <div className="composer-field">
             <label htmlFor={`${key}-to`}>To</label>
-            <RecipientInput id={`${key}-to`} value={d.to} onChange={(to) => patch({ to })} placeholder="Recipients" autoFocus={!d.to.length} />
+            <RecipientInput id={`${key}-to`} value={d.to} onChange={(to) => patch({ to })} placeholder="Recipients" autoFocus={initialFocus === "to"} />
             <span className="field-extra">
               {!d.showCc && <button type="button" onClick={() => patch({ showCc: true })}>Cc</button>}
               {!d.showBcc && <button type="button" onClick={() => patch({ showBcc: true })}>Bcc</button>}
@@ -165,13 +170,13 @@ export function Composer({ draft }: { draft: Draft }) {
           )}
           <div className="composer-field">
             <label htmlFor={`${key}-subj`} className="sr-only">Subject</label>
-            <input id={`${key}-subj`} className="plain" placeholder="Subject" value={d.subject} onChange={(e) => patch({ subject: e.target.value })} autoFocus={d.to.length > 0 && !d.subject} />
+            <input id={`${key}-subj`} className="plain" placeholder="Subject" value={d.subject} onChange={(e) => patch({ subject: e.target.value })} autoFocus={initialFocus === "subject"} />
             {d.priority !== "normal" && <span className="tag" style={{ background: d.priority === "high" ? "var(--danger)" : "var(--fg-faint)" }}>{d.priority === "high" ? "High priority" : "Low priority"}</span>}
             {d.requestReceipt && <span className="tag" style={{ background: "var(--accent)" }} title="Read receipt requested"><CheckCheck size={12} /></span>}
           </div>
         </div>
         {d.format === "html" ? (
-          <RichEditor ref={editorRef} html={d.html} onChange={onHtml} placeholder="Write your message…" spellcheck={settings.spellcheck} onFiles={(files) => addFiles(key, files)} showToolbar={showToolbar} autoFocus={d.to.length > 0 && Boolean(d.subject)} />
+          <RichEditor ref={editorRef} html={d.html} onChange={onHtml} placeholder="Write your message…" spellcheck={settings.spellcheck} onFiles={(files) => addFiles(key, files)} showToolbar={showToolbar} autoFocus={initialFocus === "body"} />
         ) : (
           <textarea className="editor-textarea" value={d.text} onChange={(e) => patch({ text: e.target.value })} placeholder="Write your message…" spellCheck={settings.spellcheck} />
         )}
@@ -230,3 +235,12 @@ export function Composer({ draft }: { draft: Draft }) {
     </div>
   );
 }
+
+export type FocusTarget = "to" | "subject" | "body";
+
+/** Which field a freshly opened composer should put the caret in. */
+export function initialFocusTarget(d: Pick<Draft, "to" | "subject">): FocusTarget {
+  if (!d.to.length) return "to";
+  if (!d.subject) return "subject";
+  return "body";
+}
diff --git a/web/src/views/compose/RichEditor.tsx b/web/src/views/compose/RichEditor.tsx
index 6c21951..93c1914 100644
--- a/web/src/views/compose/RichEditor.tsx
+++ b/web/src/views/compose/RichEditor.tsx
@@ -48,20 +48,23 @@ export const RichEditor = forwardRef<RichEditorHandle, Props>(function RichEdito
     }
   }, [html]);
 
+  // autoFocus means "focus on mount", as it does on a DOM element. Reacting to
+  // the prop turning true later yanks the caret out of whatever the user is
+  // typing in — typing the first letter of a subject used to jump to the body.
+  const autoFocusOnMount = useRef(autoFocus);
   useEffect(() => {
-    if (autoFocus) {
-      const el = elRef.current;
-      if (!el) return;
-      el.focus();
-      // caret at start
-      const sel = window.getSelection();
-      const range = document.createRange();
-      range.setStart(el, 0);
-      range.collapse(true);
-      sel?.removeAllRanges();
-      sel?.addRange(range);
-    }
-  }, [autoFocus]);
+    if (!autoFocusOnMount.current) return;
+    const el = elRef.current;
+    if (!el) return;
+    el.focus();
+    // caret at start
+    const sel = window.getSelection();
+    const range = document.createRange();
+    range.setStart(el, 0);
+    range.collapse(true);
+    sel?.removeAllRanges();
+    sel?.addRange(range);
+  }, []);
 
   const emit = useCallback(() => {
     const el = elRef.current;
diff --git a/web/src/views/compose/__tests__/focus.test.tsx b/web/src/views/compose/__tests__/focus.test.tsx
new file mode 100644
index 0000000..cc2c93b
--- /dev/null
+++ b/web/src/views/compose/__tests__/focus.test.tsx
@@ -0,0 +1,62 @@
+import { act } from "react";
+import { createRoot, type Root } from "react-dom/client";
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import { RichEditor } from "../RichEditor";
+import { initialFocusTarget } from "../Composer";
+
+(globalThis as { IS_REACT_ACT_ENVIRONMENT?: boolean }).IS_REACT_ACT_ENVIRONMENT = true;
+
+describe("initialFocusTarget", () => {
+  it("starts a blank message in the recipients", () => {
+    expect(initialFocusTarget({ to: [], subject: "" })).toBe("to");
+  });
+  it("moves on to the subject once there are recipients", () => {
+    expect(initialFocusTarget({ to: [{ name: null, email: "a@b.c" }], subject: "" })).toBe("subject");
+  });
+  it("starts a reply — addressed and titled — in the body", () => {
+    expect(initialFocusTarget({ to: [{ name: null, email: "a@b.c" }], subject: "Re: hi" })).toBe("body");
+  });
+});
+
+describe("RichEditor autoFocus", () => {
+  let host: HTMLDivElement;
+  let root: Root;
+
+  beforeEach(() => {
+    host = document.createElement("div");
+    document.body.appendChild(host);
+    root = createRoot(host);
+  });
+
+  afterEach(() => {
+    act(() => root.unmount());
+    host.remove();
+  });
+
+  const render = (autoFocus: boolean) =>
+    act(() => {
+      root.render(<RichEditor html="" onChange={() => {}} showToolbar={false} autoFocus={autoFocus} />);
+    });
+
+  const editor = () => host.querySelector<HTMLElement>('[contenteditable="true"]');
+
+  it("focuses on mount when asked to", () => {
+    render(true);
+    expect(document.activeElement).toBe(editor());
+  });
+
+  it("does not steal focus when autoFocus turns true later", () => {
+    render(false);
+    expect(document.activeElement).not.toBe(editor());
+
+    // Something else holds the caret — the subject field being typed into.
+    const subject = document.createElement("input");
+    document.body.appendChild(subject);
+    subject.focus();
+    expect(document.activeElement).toBe(subject);
+
+    render(true);
+    expect(document.activeElement, "the editor grabbed focus mid-typing").toBe(subject);
+    subject.remove();
+  });
+});