A reply to a self-addressed message follows its Reply-To (#415) (#416)

A website contact form mails the site's own address: From and To are
both info@thesite, and the person who filled the form in is in Reply-To.
Replying addressed the draft to info@thesite -- the site's own desk --
instead of to them.

The reply already knows two shapes. A message somebody sent me is
answered to its Reply-To, which is what that header is for. A message
*I* sent is answered to the people I wrote to, and deliberately not to
my own Reply-To, which is where answers to me belong and would send my
reply to myself. A contact form passes the test for the second: every
address in From is mine.

So it fell down the chain the second shape keeps for a message with
nobody obvious to answer -- To without me, then Cc, then, having run
out, every address on the message, which here was mine alone.

The Reply-To now goes in that chain, one step before the last: when no
recipient but me is left and the message names a Reply-To that is not
mine either, that address is who it is really from. Keeping it after the
Cc is what leaves a message I did send alone -- somebody I actually
wrote to still beats my own Reply-To, which is the case the existing
guard was built for and its test still holds.

No new strings.

web/src/store/__tests__/reply-addressing.test.ts

@@ -153,6 +153,30 @@ describe("a message of mine with nobody obvious to reply to", () => {
     const d = await draftFor({ ...MINE, to: [ME], cc: [] } as Email, "reply");
     expect(addrs(d.to)).toEqual([ME.email]);
   });
+
+  it("answers the Reply-To rather than my own desk when nobody else is on it", async () => {
+    /*
+     * A contact form: the site mails itself, From and To both its own address,
+     * and the person who filled the form in is in Reply-To. From alone makes
+     * this look like mine, and the fallback used to reply to me (#415).
+     */
+    const form = { ...MINE, to: [ME], cc: [], replyTo: [{ name: "Michael", email: "[email protected]" }] } as Email;
+    const d = await draftFor(form, "reply");
+    expect(addrs(d.to)).toEqual(["[email protected]"]);
+  });
+
+  it("does the same on a reply all, without cc-ing myself", async () => {
+    const form = { ...MINE, to: [ME], cc: [], replyTo: [{ name: "Michael", email: "[email protected]" }] } as Email;
+    const d = await draftFor(form, "replyAll");
+    expect(addrs(d.to)).toEqual(["[email protected]"]);
+    expect(d.cc).toEqual([]);
+  });
+
+  it("still prefers somebody I actually wrote to over my own Reply-To", async () => {
+    // The Cc is a person; the Reply-To is where answers to me belong.
+    const d = await draftFor({ ...MINE, to: [ME], replyTo: [{ name: null, email: "[email protected]" }] } as Email, "reply");
+    expect(addrs(d.to)).toEqual([BOB.email]);
+  });
 });
 
 describe("forwarding", () => {

web/src/store/compose.ts

@@ -410,6 +410,19 @@ export const useCompose = create<ComposeState>((set, get) => ({
         // Addressed only to myself, or only in Cc: there is still somebody this
         // is a reply to, and an empty To is not it.
         if (!to.length) { to = cc.length ? cc : withoutOwn(full.cc ?? []); cc = []; }
+        /*
+         * Nobody but me on the message, and a Reply-To pointing somewhere that
+         * is not mine: that address is who this is really from.
+         *
+         * A contact form is the shape of it -- From and To are both the site's
+         * own mailbox, and the person who filled the form in is in Reply-To.
+         * The address test above calls that mine, correctly as far as it goes,
+         * and the fallback then addressed the reply to my own desk (#415).
+         *
+         * After the Cc, not before it: a message I really did send carries my
+         * own Reply-To, and somebody I actually wrote to beats it.
+         */
+        if (!to.length) to = withoutOwn(full.replyTo ?? []);
         if (!to.length) to = uniqueAddresses([...(full.to ?? []), ...(full.cc ?? [])]);
       } else {
         to = uniqueAddresses(full.replyTo?.length ? full.replyTo : (full.from ?? []));