diff --git a/docs/architecture.md b/docs/architecture.md
index ad90456..d719766 100644
--- a/docs/architecture.md
+++ b/docs/architecture.md
@@ -235,6 +235,7 @@ mps_page_session (raw rows)
 | [MPS-20](tickets/mps-20.md) | Auction House Mode (eBay-style Bidding) | Complete |
 | [MPS-21](tickets/mps-21.md) | Make-an-Offer Mode | Complete |
 | [MPS-22](tickets/mps-22.md) | Kill-Switch Feature Flags — Karaoke + Torrent Off by Default | Complete |
+| [MPS-23](tickets/mps-23.md) | Consolidated Transactional Sender Identity + Shop Contact Email | Open |
 
 ## Related Docs
 
diff --git a/docs/tickets/mps-23.md b/docs/tickets/mps-23.md
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+# MPS-23 — Consolidated transactional sender identity + shop contact email
+
+**Status:** Open (DNS prep done; needs a decision on the Reply-To / shop-contact-email approach before code lands)
+
+## Problem
+
+MPS sends each shop's transactional mail (OTP login codes, purchase receipts,
+sale notifications, gift cards, offers, invites) `From: no-reply@<request.domain>`
+— i.e. from the shop's *own* hostname:
+
+- `my.makepostsell.com` → `no-reply@my.makepostsell.com`
+- `<shop>.makepostsell.com` → `no-reply@<shop>.makepostsell.com`
+- operator custom domain `shop.unturf.com` → `no-reply@shop.unturf.com`
+
+For operator custom domains, MPS controls no DKIM key for that domain and the
+domain's SPF doesn't authorize MPS's sending infrastructure, so the mail is
+**unauthenticated** (no DKIM, no SPF pass) → Gmail spam-folders it. Even
+`no-reply@my.makepostsell.com` lands in spam on first contact because
+`makepostsell.com` is a cold direct-signing identity (its mail historically
+went through Mailgun's `mg.makepostsell.com`, never `makepostsell.com` itself).
+
+Background: 2026-05-12 mail-infra work moved both origin boxes
+(`origin.makepostsell.com`, `origin.remarkbox.com`) to DKIM-sign at origin and
+relay through `mx1.foxhop.net` (warm IP). `my.makepostsell.com` / `*.makepostsell.com`
+/ `remarkbox.com` mail now passes SPF+DKIM+DMARC. Operator-custom-domain shops
+are the remaining gap, and even the makepostsell ones benefit from one
+consistent warmed identity.
+
+## Fix
+
+Send **all** MPS transactional mail from one warm, authenticated identity:
+`no-reply@origin.makepostsell.com`.
+
+- opendkim on `origin.makepostsell.com` already signs `*@*.makepostsell.com`
+  with `d=makepostsell.com` → `no-reply@origin.makepostsell.com` is signed
+  (DMARC-aligned at the `makepostsell.com` org-domain level under relaxed mode).
+- `origin.makepostsell.com` SPF record (added in `proxy.unturf.com/ingress/pdns-init.sh`):
+  `v=spf1 a a:mx1.foxhop.net -all` → authorizes the origin box + the mx1 relay.
+- Result: every shop's mail → DKIM-signed, SPF-pass, DMARC-pass, delivered
+  from mx1's warm IP — independent of which shop/domain it's for.
+
+Recipient clarity: put the shop name in the display name —
+`From: "Acme Shop" <no-reply@origin.makepostsell.com>`.
+
+## Open question — Reply-To / customer support
+
+Shops have no contact email today (`Shop` model has no email/contact column).
+If a customer replies to an OTP/receipt it hits `no-reply@…` and vanishes.
+Options:
+
+1. **Add `Shop.support_email`** (nullable) + a field in `shop-settings`; set
+   `Reply-To: <support_email>` when the operator has filled it in. Opt-in,
+   privacy-safe. *(recommended)*
+2. Catch-all `reply@origin.makepostsell.com` → forward to the shop owner's
+   account email. Requires inbound mail handling + a mapping table.
+3. Default `Reply-To` to the shop owner's user email. Simple, but leaks the
+   owner's personal address.
+
+Until decided: ship without `Reply-To` (honest — it's `no-reply@`).
+
+## Implementation
+
+- **Config:** `app.email.sender = no-reply@origin.makepostsell.com` in
+  `data/development.ini` + the prod pillar (`foxhop-pillar/uwsgi/makepostsell/init.sls`).
+  `lib/mail.py:send_pyramid_email` already reads `request.app.get("email.sender", …)`.
+- **`lib/mail.py`:** extract `_build_from_header(request, sender_email)` →
+  `email.utils.formataddr((display_name, sender_email))`, `display_name` =
+  `request.shop.name` when a shop is in context, else the site name. Add
+  `Reply-To` per the chosen option. Use the helper in `send_email`/`send_pyramid_email`.
+- **DNS (done):** `origin.makepostsell.com|TXT|v=spf1 a a:mx1.foxhop.net -all`.
+- **Optional hardening:** dedicated DKIM key for `origin.makepostsell.com`
+  (publish `<sel>._domainkey.origin.makepostsell.com`, add to opendkim) so the
+  signature is `d=origin.makepostsell.com` — author-domain-exact rather than
+  org-aligned. Marginal deliverability gain; not required.
+- If option (1): `Shop.support_email` column + Alembic migration (`server_default ''`)
+  + `shop-settings` form field + validation + the usual three-layer tests.
+- **Tests:** unit (`_build_from_header`, `Shop.support_email`), integration
+  (shop settings save), functional (settings POST, OTP flow still works).
+- **Docs:** `docs/architecture.md` ticket index, `docs/design-system.md` if a
+  new form field, `CLAUDE.md` note, portal `pricing.html`/`index.html` if
+  surfaced to users.