diff --git a/lib/api/submit.js b/lib/api/submit.js
index 47af61c9..8e35dd98 100644
--- a/lib/api/submit.js
+++ b/lib/api/submit.js
@@ -15,7 +15,7 @@ const Transform = require('stream').Transform;
 const { sessSchema, sessIPSchema, booleanSchema, metaDataSchema } = require('../schemas');
 const { preprocessAttachments } = require('../data-url');
 const { userId, mailboxId } = require('../schemas/request/general-schemas');
-const { AddressOptionalName, AddressOptionalNameArray, Header, Attachment, ReferenceWithAttachments } = require('../schemas/request/messages-schemas');
+const { AddressOptionalName, AddressOptionalNameArray, Header, ReferenceWithoutAttachments } = require('../schemas/request/messages-schemas');
 const { successRes } = require('../schemas/response/general-schemas');
 
 class StreamCollect extends Transform {
@@ -631,7 +631,7 @@ module.exports = (db, server, messageHandler, userHandler, settingsHandler) => {
             description: 'Use this method to send emails from a user account',
             validationObjs: {
                 requestBody: {
-                    mailbox: mailboxId,
+                    mailbox: Joi.string().hex().lowercase().length(24).description('ID of the Mailbox'),
                     from: AddressOptionalName.description('Addres for the From: header'),
                     replyTo: AddressOptionalName.description('Address for the Reply-To: header'),
                     to: Joi.array()
@@ -664,12 +664,27 @@ module.exports = (db, server, messageHandler, userHandler, settingsHandler) => {
                         .empty('')
                         .max(1024 * 1024)
                         .description('HTML formatted message'),
-                    attachments: Joi.array().items(Attachment).description('Attachments for the message'),
+                    attachments: Joi.array()
+                        .items(
+                            Joi.object({
+                                filename: Joi.string().empty('').max(255).description('Attachment filename'),
+                                contentType: Joi.string().empty('').max(255).description('MIME type for the attachment file'),
+                                encoding: Joi.string().empty('').default('base64').description('Encoding to use to store the attachments'),
+                                contentTransferEncoding: Joi.string().empty('').description('Transfer encoding'),
+                                contentDisposition: Joi.string().empty('').trim().lowercase().valid('inline', 'attachment').description('Content Disposition'),
+                                content: Joi.string().required().description('Base64 encoded attachment content'),
+                                cid: Joi.string()
+                                    .empty('')
+                                    .max(255)
+                                    .description('Content-ID value if you want to reference to this attachment from HTML formatted message')
+                            })
+                        )
+                        .description('Attachments for the message'),
 
                     meta: metaDataSchema.label('metaData').description('Optional metadata, must be an object or JSON formatted string'),
                     sess: sessSchema,
                     ip: sessIPSchema,
-                    reference: ReferenceWithAttachments.description(
+                    reference: ReferenceWithoutAttachments.description(
                         'Optional referenced email. If uploaded message is a reply draft and relevant fields are not provided then these are resolved from the message to be replied to'
                     ),
                     // if true then treat this message as a draft
diff --git a/lib/schemas/request/messages-schemas.js b/lib/schemas/request/messages-schemas.js
index 48de170c..12c53d89 100644
--- a/lib/schemas/request/messages-schemas.js
+++ b/lib/schemas/request/messages-schemas.js
@@ -30,7 +30,8 @@ const Attachment = Joi.object({
     encoding: Joi.string().empty('').default('base64').description('Encoding to use to store the attachments'),
     contentTransferEncoding: Joi.string().empty('').description('Transfer encoding'),
     content: Joi.string().required().description('Base64 encoded attachment content'),
-    cid: Joi.string().empty('').max(255).description('Content-ID value if you want to reference to this attachment from HTML formatted message')
+    cid: Joi.string().empty('').max(255).description('Content-ID value if you want to reference to this attachment from HTML formatted message'),
+    contentDisposition: Joi.string().empty('').trim().lowercase().valid('inline', 'attachment').description('Content Disposition')
 }).$_setFlag('objectName', 'Attachment');
 
 const ReferenceWithAttachments = Joi.object({
@@ -51,6 +52,12 @@ const ReferenceWithAttachments = Joi.object({
         )
 }).$_setFlag('objectName', 'ReferenceWithAttachments');
 
+const ReferenceWithoutAttachments = Joi.object({
+    mailbox: mailboxId,
+    id: messageId,
+    action: Joi.string().valid('reply', 'replyAll', 'forward').required().description('Either reply, replyAll or forward')
+}).$_setFlag('objectName', 'Reference');
+
 const Bimi = Joi.object({
     domain: Joi.string().domain().required().description('Domain name for the BIMI record. It does not have to be the same as the From address.'),
     selector: Joi.string().empty('').max(255).description('Optional BIMI selector')
@@ -63,5 +70,6 @@ module.exports = {
     Header,
     Attachment,
     ReferenceWithAttachments,
-    Bimi
+    Bimi,
+    ReferenceWithoutAttachments
 };