diff --git a/app/main.py b/app/main.py
index 0d843bc..69b4602 100644
--- a/app/main.py
+++ b/app/main.py
@@ -142,6 +142,10 @@ SMTP_USERNAME = os.environ.get("CLOUDRON_MAIL_SMTP_USERNAME", "")
 SMTP_PASSWORD = os.environ.get("CLOUDRON_MAIL_SMTP_PASSWORD", "")
 MAIL_FROM = os.environ.get("CLOUDRON_MAIL_FROM", "info@inference.coop")
 MAIL_FROM_NAME = os.environ.get("CLOUDRON_MAIL_FROM_DISPLAY_NAME", "Inference Cooperative")
+# Reply-to address. The sendmail addon only authorizes sending from the app's
+# own address (portal.app@inference.coop), so the From header is pinned there;
+# we set Reply-To so member replies land at the co-op inbox instead.
+MAIL_REPLY_TO = os.environ.get("MAIL_REPLY_TO", "info@inference.coop")
 # Public base URL for the portal (used in email links).
 PORTAL_BASE = os.environ.get("PORTAL_BASE", "https://portal.inference.coop")
 
@@ -284,6 +288,7 @@ def send_email(to: str, subject: str, text_body: str, html_body: str | None = No
         msg["From"] = f"{MAIL_FROM_NAME} <{MAIL_FROM}>"
         msg["To"] = to
         msg["Subject"] = subject
+        msg["Reply-To"] = MAIL_REPLY_TO
         msg.attach(MIMEText(text_body, "plain", "utf-8"))
         if html_body:
             msg.attach(MIMEText(html_body, "html", "utf-8"))