Hi @JimmyWork
You need to use following structure in html field when sending adaptive card using send email action:
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<script type="application/adaptivecard+json">{
"type": "AdaptiveCard",
"version": "1.2",
"hideOriginalBody": true,
<body tag of adaptive card from adaptive designer>
}
</script>
</head>
<body>
Visit the <a href="https://docs.microsoft.com/outlook/actionable-messages">Outlook Dev Portal</a> to learn more about Actionable Messages.
</body>
</html>

Here is full html with card:
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<script type="application/adaptivecard+json">{
"type": "AdaptiveCard",
"version": "1.2",
"hideOriginalBody": false,
"body": [
{
"type": "TextBlock",
"text": "Publish Adaptive Card schema",
"weight": "Bolder",
"size": "Medium"
},
{
"type": "ColumnSet",
"columns": [
{
"type": "Column",
"width": "auto",
"items": [
{
"type": "Image",
"url": "https://pbs.twimg.com/profile_images/3647943215/d7f12830b3c17a5a9e4afcc370e3a37e_400x400.jpeg",
"size": "Small",
"style": "Person"
}
]
},
{
"type": "Column",
"width": "stretch",
"items": [
{
"type": "TextBlock",
"text": "Matt Hidinger",
"weight": "Bolder",
"wrap": true
},
{
"type": "TextBlock",
"spacing": "None",
"text": "Created {{DATE(2017-02-14T06:08:39Z, SHORT)}}",
"isSubtle": true,
"wrap": true
}
]
}
]
},
{
"type": "TextBlock",
"text": "Now that we have defined the main rules and features of the format, we need to produce a schema and publish it to GitHub. The schema will be the starting point of our reference documentation.",
"wrap": true
},
{
"type": "FactSet",
"facts": [
{
"title": "Board:",
"value": "Adaptive Card"
},
{
"title": "List:",
"value": "Backlog"
},
{
"title": "Assigned to:",
"value": "Matt Hidinger"
},
{
"title": "Due date:",
"value": "Not set"
}
]
}
],
"actions": [
{
"type": "Action.ShowCard",
"title": "Set due date",
"card": {
"type": "AdaptiveCard",
"body": [
{
"type": "Input.Date",
"id": "dueDate"
}
],
"actions": [
{
"type": "Action.Submit",
"title": "OK"
}
],
"$schema": "http://adaptivecards.io/schemas/adaptive-card.json"
}
},
{
"type": "Action.ShowCard",
"title": "Comment",
"card": {
"type": "AdaptiveCard",
"body": [
{
"type": "Input.Text",
"id": "comment",
"isMultiline": true,
"placeholder": "Enter your comment"
}
],
"actions": [
{
"type": "Action.Submit",
"title": "OK"
}
],
"$schema": "http://adaptivecards.io/schemas/adaptive-card.json"
}
}
]
}
</script>
</head>
<body>
Visit the <a href="https://docs.microsoft.com/outlook/actionable-messages">Outlook Dev Portal</a> to learn more about Actionable Messages.
</body>
</html>
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