diff --git a/CLAUDE.md b/CLAUDE.md
index 3a44507..afc48c6 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -164,4 +164,10 @@ Nav items come from Drupal's `main` menu. Items titled `"Book An Appointment"` o
 
 ## Email
 
-Booking confirmation emails are sent via `riverside_pt_mail()` in `.module` using the `booking_request` key. Transport is Postmark, configured in `config/sync/symfony_mailer.mailer_transport.postmark.yml`. The API key is injected via the `POSTMARK_API_KEY` environment variable.
+Booking confirmation emails are sent via `riverside_pt_mail()` in `.module` using the `booking_request` key. Transport is Postmark (via `drupal/symfony_mailer`), configured in `config/sync/symfony_mailer.mailer_transport.postmark.yml`. The API key is injected via the `POSTMARK_API_KEY` environment variable.
+
+In `settings.php` (when the key is present) we also force:
+- `mailer_transport.settings.default_transport = postmark`
+- `system.mail.interface.default = symfony_mailer`
+
+On localhost/dev, a fake sendmail binary is provided (via Dockerfile + entrypoint) that prints the full email to stderr (visible via `docker compose logs`) instead of failing with "sh: 1: /usr/sbin/sendmail: not found". This catches any legacy `php_mail` fallbacks. Real transactional mail goes through Postmark when configured.
diff --git a/Dockerfile b/Dockerfile
index 426f37e..d2ef41b 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -78,7 +78,9 @@ COPY docker/nginx/default.conf /etc/nginx/conf.d/default.conf.template
 
 COPY docker/supervisord.conf /etc/supervisor/conf.d/supervisord.conf
 COPY docker/php/entrypoint.sh /entrypoint.sh
-RUN chmod +x /entrypoint.sh
+COPY docker/php/fake-sendmail.sh /usr/local/bin/fake-sendmail.sh
+RUN chmod +x /entrypoint.sh /usr/local/bin/fake-sendmail.sh && \
+    echo 'sendmail_path = /usr/local/bin/fake-sendmail.sh' > /usr/local/etc/php/conf.d/sendmail.ini
 
 RUN chown -R www-data:www-data web/sites/default/files && \
     chmod -R 755 web/sites/default/files && \
diff --git a/docker/php/entrypoint.sh b/docker/php/entrypoint.sh
index 86a143d..04424a3 100644
--- a/docker/php/entrypoint.sh
+++ b/docker/php/entrypoint.sh
@@ -65,6 +65,28 @@ npm run build --prefix /var/www/html >/dev/null 2>&1 && echo "[entrypoint] Tailw
 
 $DRUSH cache:rebuild >/dev/null 2>&1 && echo "[entrypoint] Cache rebuilt."
 
+# Mock sendmail on localhost/dev: prints full email to stderr (visible in docker logs)
+# instead of erroring with "sh: 1: /usr/sbin/sendmail: not found".
+# This catches any php_mail / legacy mail() calls (e.g. some webforms, fallbacks).
+# Real emails should still go via symfony_mailer + Postmark when configured.
+if [ ! -x /usr/local/bin/fake-sendmail.sh ]; then
+  cat > /usr/local/bin/fake-sendmail.sh << 'FAKE_SENDMAIL'
+#!/bin/sh
+echo "=== MOCK SENDMAIL (dev - email logged, not sent) ===" >&2
+echo "Timestamp: $(date -Iseconds)" >&2
+echo "Called as: $0 $*" >&2
+echo "----- EMAIL CONTENT -----" >&2
+cat >&2
+echo "" >&2
+echo "=== END MOCK SENDMAIL ===" >&2
+exit 0
+FAKE_SENDMAIL
+  chmod +x /usr/local/bin/fake-sendmail.sh
+  echo "[entrypoint] Installed fake sendmail for dev logging."
+fi
+# Override sendmail_path for PHP (affects php_mail interface and any direct mail()).
+echo 'sendmail_path = /usr/local/bin/fake-sendmail.sh' > /usr/local/etc/php/conf.d/sendmail.ini 2>/dev/null || true
+
 if [ "${DEBUG:-false}" = "true" ]; then
   NGINX_CSS_CACHE='expires off; add_header Cache-Control "no-store";'
 else
diff --git a/docker/php/fake-sendmail.sh b/docker/php/fake-sendmail.sh
new file mode 100755
index 0000000..5eeb725
--- /dev/null
+++ b/docker/php/fake-sendmail.sh
@@ -0,0 +1,15 @@
+#!/bin/sh
+# Fake sendmail for local development.
+# Instead of delivering email, it prints the entire message to stderr
+# so it appears in `docker compose logs`.
+# This prevents "sh: 1: /usr/sbin/sendmail: not found" errors.
+
+echo "=== MOCK SENDMAIL: email would have been sent (logged instead) ===" >&2
+echo "Timestamp: $(date -Iseconds)" >&2
+echo "Args: $*" >&2
+echo "----------------------------------------" >&2
+cat >&2
+echo "" >&2
+echo "=== END MOCK SENDMAIL ===" >&2
+
+exit 0
diff --git a/web/modules/custom/riverside_pt/js/components/rpt-booking.js b/web/modules/custom/riverside_pt/js/components/rpt-booking.js
index 6c18670..63d8418 100644
--- a/web/modules/custom/riverside_pt/js/components/rpt-booking.js
+++ b/web/modules/custom/riverside_pt/js/components/rpt-booking.js
@@ -318,9 +318,15 @@ function BookingPanel({ service, settings, onServiceChange }) {
         setFormData(EMPTY_FORM);
       } else {
         setSubmitting(false);
-        setSubmitError(res.status === 422
-          ? "That slot was just booked. Please choose another time."
-          : "Something went wrong. Please try again.");
+        if (res.status === 422) {
+          setSubmitError("That slot was just booked. Please choose another time.");
+        } else {
+          res.json().then(function (data) {
+            setSubmitError(data.message || "Something went wrong. Please try again.");
+          }).catch(function () {
+            setSubmitError("Something went wrong. Please try again.");
+          });
+        }
       }
     }).catch(function () {
       setSubmitting(false);
diff --git a/web/modules/custom/riverside_pt/src/Controller/ScheduleController.php b/web/modules/custom/riverside_pt/src/Controller/ScheduleController.php
index 2e54297..0bcc6c4 100644
--- a/web/modules/custom/riverside_pt/src/Controller/ScheduleController.php
+++ b/web/modules/custom/riverside_pt/src/Controller/ScheduleController.php
@@ -84,7 +84,16 @@ class ScheduleController extends ControllerBase {
       if ($sent['result']) {
         return new JsonResponse(['ok' => TRUE]);
       }
-      return new JsonResponse(['error' => 'mail_failed'], 500);
+
+      \Drupal::logger('riverside_pt')->error('Booking request email failed to send to @to (user: @email)', [
+        '@to' => $to,
+        '@email' => $email,
+      ]);
+
+      return new JsonResponse([
+        'error' => 'mail_failed',
+        'message' => 'We were unable to send the confirmation email. Please try again or contact us directly to book.',
+      ], 500);
     }
 
     // Legacy/minimal path (no contact details): just stash in tempstore (for any
diff --git a/web/sites/default/settings.php b/web/sites/default/settings.php
index bc8fa9e..0c929a9 100644
--- a/web/sites/default/settings.php
+++ b/web/sites/default/settings.php
@@ -24,6 +24,19 @@ if ($postmark_key = getenv('POSTMARK_API_KEY')) {
     'postmark+api://' . $postmark_key . '@default';
 }
 
+// On localhost/DEBUG, use the core 'php_mail' interface (which respects sendmail_path
+// from php.ini, overridden to our fake-sendmail.sh that logs the email to console
+// and always succeeds). This guarantees booking requests never fail with
+// "mail_failed" during development.
+// In non-DEBUG (production), use symfony_mailer + Postmark.
+$is_dev = (bool) getenv('DEBUG');
+if ($is_dev) {
+  $config['system.mail']['interface']['default'] = 'php_mail';
+} elseif ($postmark_key) {
+  $config['mailer_transport.settings']['default_transport'] = 'postmark';
+  $config['system.mail']['interface']['default'] = 'symfony_mailer';
+}
+
 // Disable CSS/JS aggregation — assets served directly from source paths.
 $config['system.performance']['css']['preprocess'] = FALSE;
 $config['system.performance']['js']['preprocess'] = FALSE;