Shortcodes in your posts are removed
MailPoet's visual editor currently removes all shortcodes it finds in the posts you insert in your newsletter.
Shortcodes insert HTML and styles that are too often not compatible with email clients, such Gmail, Yahoo, Outlook, iPhones, etc.
Build your own shortcodes for MailPoet
MailPoet can still display custom shortcodes.
Here are instructions to build your own MailPoet-ready shortcodes.
What are shortcodes?
Shortcodes in WordPress are little snippets that add all sorts of different things, like form, boxes, images, etc. in your posts.
They look like this: [myshortcode]
See all the plugins plugins on wordpress.org that are tagged with shortcode.