Feature: Add support for sending inline attachments via HTTP API (#399)

Optional settings for Attachment ContentID & ContentType

server/ui/api/v1/swagger.json

@@ -1634,12 +1634,22 @@
               "Content": {
                 "description": "Base64-encoded string of the file content",
                 "type": "string",
-                "example": "VGhpcyBpcyBhIHBsYWluIHRleHQgYXR0YWNobWVudA=="
+                "example": "iVBORw0KGgoAAAANSUhEUgAAAEEAAAA8CAMAAAAOlSdoAAAACXBIWXMAAAHrAAAB6wGM2bZBAAAAS1BMVEVHcEwRfnUkZ2gAt4UsSF8At4UtSV4At4YsSV4At4YsSV8At4YsSV4At4YsSV4sSV4At4YsSV4At4YtSV4At4YsSV4At4YtSV8At4YsUWYNAAAAGHRSTlMAAwoXGiktRE5dbnd7kpOlr7zJ0d3h8PD8PCSRAAACWUlEQVR42pXT4ZaqIBSG4W9rhqQYocG+/ys9Y0Z0Br+x3j8zaxUPewFh65K+7yrIMeIY4MT3wPfEJCidKXEMnLaVkxDiELiMz4WEOAZSFghxBIypCOlKiAMgXfIqTnBgSm8CIQ6BImxEUxEckClVQiHGj4Ba4AQHikAIClwTE9KtIghAhUJwoLkmLnCiAHJLRKgIMsEtVUKbBUIwoAg2C4QgQBE6l4VCnApBgSKYLLApCnCa0+96AEMW2BQcmC+Pr3nfp7o5Exy49gIADcIqUELGfeA+bp93LmAJp8QJoEcN3C7NY3sbVANixMyI0nku20/n5/ZRf3KI2k6JEDWQtxcbdGuAqu3TAXG+/799Oyyas1B1MnMiA+XyxHp9q0PUKGPiRAau1fZbLRZV09wZcT8/gHk8QQAxXn8VgaDqcUmU6O/r28nbVwXAqca2mRNtPAF5+zoP2MeN9Fy4NgC6RfcbgE7XITBRYTtOE3U3C2DVff7pk+PkUxgAbvtnPXJaD6DxulMLwOhPS/M3MQkgg1ZFrIXnmfaZoOfpKiFgzeZD/WuKqQEGrfJYkyWf6vlG3xUgTuscnkNkQsb599q124kdpMUjCa/XARHs1gZymVtGt3wLkiFv8rUgTxitYCex5EVGec0Y9VmoDTFBSQte2TfXGXlf7hbdaUM9Sk7fisEN9qfBBTK+FZcvM9fQSdkl2vj4W2oX/bRogO3XasiNH7R0eW7fgRM834ImTg+Lg6BEnx4vz81rhr+MYPBBQg1v8GndEOrthxaCTxNAOut8WKLGZQl+MPz88Q9tAO/hVuSeqQAAAABJRU5ErkJggg=="
+              },
+              "ContentID": {
+                "description": "Optional Content-ID (`cid`) for attachment.\nIf this field is set then the file is attached inline.",
+                "type": "string",
+                "example": "mailpit-logo"
+              },
+              "ContentType": {
+                "description": "Optional Content Type for the the attachment.\nIf this field is not set (or empty) then the content type is automatically detected.",
+                "type": "string",
+                "example": "image/png"
               },
               "Filename": {
                 "description": "Filename",
                 "type": "string",
-                "example": "AttachedFile.txt"
+                "example": "mailpit.png"
               }
             }
           }
@@ -1698,7 +1708,7 @@
         "HTML": {
           "description": "Message body (HTML)",
           "type": "string",
-          "example": "\u003cp style=\"font-family: arial\"\u003eMailpit is \u003cb\u003eawesome\u003c/b\u003e!\u003c/p\u003e"
+          "example": "\u003cdiv style=\"text-align:center\"\u003e\u003cp style=\"font-family: arial; font-size: 24px;\"\u003eMailpit is \u003cb\u003eawesome\u003c/b\u003e!\u003c/p\u003e\u003cp\u003e\u003cimg src=\"cid:mailpit-logo\" /\u003e\u003c/p\u003e\u003c/div\u003e"
         },
         "Headers": {
           "description": "Optional headers in {\"key\":\"value\"} format",
@@ -1751,7 +1761,7 @@
         "Text": {
           "description": "Message body (text)",
           "type": "string",
-          "example": "This is the text body"
+          "example": "Mailpit is awesome!"
         },
         "To": {
           "description": "\"To\" recipients",