diff --git a/env.d/development/mta-in.defaults b/env.d/development/mta-in.defaults
index 43c37868..76c0f902 100644
--- a/env.d/development/mta-in.defaults
+++ b/env.d/development/mta-in.defaults
@@ -1,4 +1,4 @@
 MDA_API_BASE_URL=http://backend-dev:8000/api/v1.0/
 MDA_API_SECRET=my-shared-secret-mda
 MDA_API_TIMEOUT=2
-MESSAGE_SIZE_LIMIT=30000000
+MAX_INCOMING_EMAIL_SIZE=30000000
diff --git a/env.d/development/mta-out.defaults b/env.d/development/mta-out.defaults
index 623f9abd..bd1dbf37 100644
--- a/env.d/development/mta-out.defaults
+++ b/env.d/development/mta-out.defaults
@@ -6,7 +6,7 @@ SMTP_USERNAME=user
 SMTP_PASSWORD=pass
 
 # Optional: Message Size Limit
-# MESSAGE_SIZE_LIMIT=10240000
+# MAX_INCOMING_EMAIL_SIZE=10240000
 
 # POSTFIX_DEBUG=1
 
diff --git a/src/mta-in/entrypoint.sh b/src/mta-in/entrypoint.sh
index ecabb864..8ce5def7 100644
--- a/src/mta-in/entrypoint.sh
+++ b/src/mta-in/entrypoint.sh
@@ -15,7 +15,7 @@ echo >> /etc/postfix/main.cf
 [[ -n "${MYHOSTNAME}" ]] && echo "myhostname = ${MYHOSTNAME}" >> /etc/postfix/main.cf
 [[ -n "${MYORIGIN}" ]] && echo "myorigin = ${MYORIGIN}" >> /etc/postfix/main.cf
 [[ -n "${MYDOMAIN}" ]] && echo "mydomain = ${MYDOMAIN}" >> /etc/postfix/main.cf
-echo "message_size_limit=${MESSAGE_SIZE_LIMIT:-10240000}" >> /etc/postfix/main.cf
+echo "message_size_limit=${MAX_INCOMING_EMAIL_SIZE:-10240000}" >> /etc/postfix/main.cf
 
 if [ "${ENABLE_PROXY_PROTOCOL:-false}" = "haproxy" ]; then
   echo "postscreen_upstream_proxy_protocol = haproxy" >> /etc/postfix/main.cf
diff --git a/src/mta-out/README.md b/src/mta-out/README.md
index 97bc4b8c..3c2e3497 100644
--- a/src/mta-out/README.md
+++ b/src/mta-out/README.md
@@ -35,7 +35,7 @@ Configuration is done entirely through environment variables:
 - `MYHOSTNAME`: The hostname this MTA identifies itself with in HELO/EHLO commands (default: `localhost`). Setting a proper FQDN is recommended. If it is not set we will attempt auto-detection from the rRNS of the host.
 - `TLS_CERT_PATH`: Path to the TLS certificate file (default: `/etc/ssl/certs/ssl-cert-snakeoil.pem`). **WARNING:** Mount a real certificate in production.
 - `TLS_KEY_PATH`: Path to the TLS private key file (default: `/etc/ssl/private/ssl-cert-snakeoil.key`). **WARNING:** Mount a real key in production.
-- `MESSAGE_SIZE_LIMIT`: Maximum size of messages in bytes (default: `10240000`).
+- `MAX_INCOMING_EMAIL_SIZE`: Maximum size of messages in bytes (default: `10240000`).
 
 ## Testing
 
diff --git a/src/mta-out/entrypoint.sh b/src/mta-out/entrypoint.sh
index ecb9a390..9e139d21 100644
--- a/src/mta-out/entrypoint.sh
+++ b/src/mta-out/entrypoint.sh
@@ -18,7 +18,7 @@ cp /app/etc/sasl/smtpd.conf /etc/postfix/sasl/smtpd.conf
 : "${SMTP_PASSWORD:?Error: SMTP_PASSWORD must be set}"
 
 # Set optional vars with defaults
-export MESSAGE_SIZE_LIMIT=${MESSAGE_SIZE_LIMIT:-10240000}
+export MAX_INCOMING_EMAIL_SIZE=${MAX_INCOMING_EMAIL_SIZE:-10240000}
 export SMTP_RELAY_HOST=${SMTP_RELAY_HOST:-""}
 export SMTP_RELAY_USERNAME=${SMTP_RELAY_USERNAME:-""}
 export SMTP_RELAY_PASSWORD=${SMTP_RELAY_PASSWORD:-""}
diff --git a/src/mta-out/etc/main.cf.j2 b/src/mta-out/etc/main.cf.j2
index caceebf9..74bc6f31 100644
--- a/src/mta-out/etc/main.cf.j2
+++ b/src/mta-out/etc/main.cf.j2
@@ -75,7 +75,7 @@ smtpd_relay_restrictions =
    reject
 
 # === Message Size ===
-message_size_limit = {{ MESSAGE_SIZE_LIMIT }}
+message_size_limit = {{ MAX_INCOMING_EMAIL_SIZE }}
 
 # === Delivery Method (Outgoing Connections) ===
 {% if SMTP_RELAY_HOST %}