diff --git a/docker-compose.override.yml b/docker-compose.override.yml
new file mode 100644
index 000000000..0df5310a2
--- /dev/null
+++ b/docker-compose.override.yml
@@ -0,0 +1,9 @@
+version: '3.7'
+services:
+    emailengine:
+        build: .
+        ports:
+            # API and web interface
+            - '3000:3000'
+            # SMTP for message submission
+            - '2525:2525'
diff --git a/workers/api.js b/workers/api.js
index 5dca38e64..565d11cda 100644
--- a/workers/api.js
+++ b/workers/api.js
@@ -2223,7 +2223,7 @@ When making API calls remember that requests against the same account are queued
 
                     bcc: Joi.array().items(addressSchema).description('List of addresses').label('AddressList'),
 
-                    subject: Joi.string().max(1024).example('What a wonderful message').description('Message subject'),
+                    subject: Joi.string().allow('', null).default('').max(1024).example('What a wonderful message').description('Message subject'),
 
                     text: Joi.string().max(MAX_ATTACHMENT_SIZE).example('Hello from myself!').description('Message Text'),
 
@@ -2879,7 +2879,7 @@ When making API calls remember that requests against the same account are queued
                         )
                         .label('RFC822Raw'),
 
-                    subject: Joi.string().max(1024).example('What a wonderful message').description('Message subject'),
+                    subject: Joi.string().allow('', null).default('').max(1024).example('What a wonderful message').description('Message subject'),
 
                     text: Joi.string().max(MAX_ATTACHMENT_SIZE).example('Hello from myself!').description('Message Text'),