diff --git a/docker-compose.qa.yml b/docker-compose.qa.yml
index 161f728..a8e48f1 100644
--- a/docker-compose.qa.yml
+++ b/docker-compose.qa.yml
@@ -37,6 +37,13 @@
 #   QA_SMTP_USER    — Brevo SMTP login. Named QA_ for the same reason as the
 #   QA_SMTP_PASSWORD  database password: pasting production's variables in here
 #   QA_SMTP_FROM      must not silently work.
+#
+#   Optional, each defaulting to the Brevo value it used to be hardcoded to, so
+#   QA can be aimed at another relay without editing this file:
+#   QA_SMTP_HOST    — default smtp-relay.brevo.com
+#   QA_SMTP_PORT    — default 587
+#   QA_SMTP_SECURE  — default false. Brevo is STARTTLS on 587, so this stays
+#                     false unless the relay is changed to an implicit-TLS one.
 #   ADMIN_GATE_SECRET — the shared secret Nginx Proxy Manager injects as the
 #                     X-Admin-Gate header on the gated location. Both sides must
 #                     hold the same value or the admin API returns 403. See #63.
@@ -80,13 +87,17 @@ services:
       # flows — verification, password reset, favorite-sold alerts and the
       # cart-reminder cron — cannot be regression tested without it. See #87.
       #
-      # Host, port and secure are not secrets and are pinned here rather than
-      # inherited: the mailer's fallbacks are Gmail's (smtp.gmail.com, 465,
-      # TLS) and Brevo needs 587 with STARTTLS, which is why SMTP_SECURE is
-      # false. Getting these wrong fails at send time, not at boot.
-      - SMTP_HOST=smtp-relay.brevo.com
-      - SMTP_PORT=587
-      - SMTP_SECURE=false
+      # Host, port and secure are not secrets, and they are now settable from
+      # the stack so QA can be pointed at a different relay without editing this
+      # file. Each keeps the Brevo value as its default rather than being left
+      # to fall through: the mailer's own fallbacks are Gmail's (smtp.gmail.com,
+      # 465, TLS) and Brevo needs 587 with STARTTLS, so an unset variable with
+      # no default here would silently aim QA at Gmail and fail at send time
+      # rather than at boot. `:-` supplies the default only when the variable is
+      # unset or empty, so setting one still wins.
+      - SMTP_HOST=${QA_SMTP_HOST:-smtp-relay.brevo.com}
+      - SMTP_PORT=${QA_SMTP_PORT:-587}
+      - SMTP_SECURE=${QA_SMTP_SECURE:-false}
       - SMTP_USER=${QA_SMTP_USER}
       - SMTP_PASSWORD=${QA_SMTP_PASSWORD}
       - SMTP_FROM=${QA_SMTP_FROM}