fix(inline): Use 'inline' as the default Content Dispostion value for embedded images

Author: andris9

examples/pool-mx.js

@@ -1,6 +1,6 @@
 'use strict';
 
-let nodemailer = require('nodemailer');
+let nodemailer = require('../lib/nodemailer');
 
 /* --- Select AWS SDK version by uncommenting correct version --- */
 

examples/ses.js

@@ -91,9 +91,13 @@ class MailComposer {
                 attachment = this._processDataUrl(attachment);
             }
 
+            let contentType = attachment.contentType || mimeFuncs.detectMimeType(attachment.filename || attachment.path || attachment.href || 'bin');
+            let isImage = /^image\//i.test(contentType);
+            let contentDisposition = attachment.contentDisposition || (isMessageNode || (isImage && attachment.cid) ? 'inline' : 'attachment');
+
             data = {
-                contentType: attachment.contentType || mimeFuncs.detectMimeType(attachment.filename || attachment.path || attachment.href || 'bin'),
-                contentDisposition: attachment.contentDisposition || (isMessageNode ? 'inline' : 'attachment'),
+                contentType,
+                contentDisposition,
                 contentTransferEncoding: 'contentTransferEncoding' in attachment ? attachment.contentTransferEncoding : 'base64'
             };
 
@@ -506,7 +510,10 @@ class MailComposer {
         }
 
         if (!/^text\//i.test(element.contentType) || element.contentDisposition) {
-            node.setHeader('Content-Disposition', element.contentDisposition || (element.cid ? 'inline' : 'attachment'));
+            node.setHeader(
+                'Content-Disposition',
+                element.contentDisposition || (element.cid && /^image\//i.test(element.contentType) ? 'inline' : 'attachment')
+            );
         }
 
         if (typeof element.content === 'string' && !['utf8', 'usascii', 'ascii'].includes(encoding)) {