KoltrixMCP Apps cards for email: what you see and how Send works
Koltrix shows four interactive cards in apps that support MCP Apps. What each does, why they are inert, how the Send button works, and what to do without one.
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Ask an assistant about your inbox and, until recently, the answer came back as a paragraph of text. Ask it to draft a reply and you got the reply as text too, plus a link.
A newer extension to MCP lets a tool's result show up as a small interactive card inside the conversation: a list you can scroll, a draft with buttons. It is called MCP Apps, and Koltrix supports it. This post explains what the cards are, which four Koltrix shows, how the Send button works, and what to do when no card appears.
What MCP Apps is
MCP, the Model Context Protocol, lets an assistant call tools. MCP Apps is an extension that lets a tool also hand the assistant app a small page to display with the result, shown in a sandbox inside the chat. The assistant app decides whether it supports this. If it does not, nothing breaks: the same tools return the same results as text.
That last point is important. Cards are an enhancement, not a requirement. Everything in your Koltrix connection works in text-only apps such as Claude Code. Cards only appear when the app tells Koltrix, at connection time, that it supports them. If it says nothing, Koltrix sends text.
The four cards
Koltrix shows four cards, each tied to specific tools.
| Card | Appears for | What you can do |
|---|---|---|
| Mailbox picker | list_mailboxes |
Pick which mailbox the assistant drafts from. Your choice goes back to the conversation as a message |
| Conversation list | search_mail, list_threads, get_inbox_summary |
See sender, subject, snippet, time, unread dot and labels, and open a conversation in Koltrix |
| Conversation | get_thread |
Read the messages as plain text, with attachments listed by name and size |
| Draft review | create_draft |
See From, To, Cc, Subject and the whole message, then Send, Edit in Koltrix or Discard |
A few details from how they are built, because they affect what you see:
- The list shows five conversations and then a "show more" control, and the conversation card shows the newest five messages with an option to show earlier ones.
- Long messages are clamped, with a way to expand them.
- A note on the conversation card says the text was written by the senders and is shown as plain text, and that links and images are not loaded.
- The cards follow your app's light or dark theme.
Why the cards are plain on purpose
Every message in your mailbox was written by someone, and a card is a web page. Putting the two together carelessly would be an invitation: a hostile subject line that runs code, or a tracking image that reports when you looked at it.
So Koltrix's cards are deliberately inert. They load nothing from the internet, no fonts, images or scripts, and make no network requests of their own. Anything that came from an email is shown as plain text. They open links only by asking your app, and only to Koltrix. The one tool a card can call is the draft card's Send, covered next. A card cannot do more than display, open a Koltrix link, and, on the draft card, press that one button.
The Send button
This is the part most worth understanding.
Sending through an assistant is off by default. If an admin has turned it on and you ticked Also allow sending email when you connected, then in an app that shows cards the draft card includes a Send button, and clicking it is the confirmation. In such an app, the assistant is not given a send tool at all. It can write the draft, and only you can send it.
Under the hood, the button calls a tool the app hides from the assistant, using a one-time token Koltrix issued with the draft:
- The token is delivered to the card rather than to the assistant's text.
- It works for 30 minutes and belongs to that draft, that connection and the exact subject, recipients and text you saw.
- It is used up by the send.
- If the draft is edited after the card appeared, or the card is older than 30 minutes, Send is refused and the card tells you to open the draft in Koltrix.
Every other check still applies: the send permission, the workspace setting (turning it off blocks the next click), your access to the From mailbox, the limits of 10 recipients, 20 sends a day per connection and 50 per workspace, no Bcc or attachments, billing and quota, and a single send per draft. The message goes out immediately and appears in Sent. Safe sending from Claude goes through the text version of the same gates.
The card shows clear states: Sending, then Sent with a link to your Sent folder, or the reason it was refused. When sending is off, it says so and offers Open in Koltrix instead of a Send button.
Discard deletes nothing. It closes the card and tells the conversation the draft was not sent. The draft stays in your Drafts, and no assistant tool can delete mail.
Which apps show cards
Anthropic documents MCP Apps support for Claude on the web, in Claude Desktop and on mobile, and OpenAI documents it for ChatGPT. Claude may ask you to allow the app to display a card the first time. Claude Code shows text. Other apps vary. Whether a particular app draws a card is that app's decision, and its behavior can change between versions, so treat this list as a guide rather than a promise.
We tested the cards in a browser against the reference host from the MCP Apps project and with a mock host. That shows the cards work as specified, but it is not the same as watching each commercial app render them, and we say so rather than imply otherwise.
When no card appears
| What you see | What it means | What to do |
|---|---|---|
| Text only | Your app does not support cards | Nothing is wrong. Use the text workflow |
| Text only, but you expected a card | You declined the app's prompt, or an organization turned interactive connectors off | Allow it in the app, or ask an admin |
| A card, but no Send button | Sending is off for the workspace or you did not tick the box | Open the draft in Koltrix and send it there |
| "Expired" or "draft changed" | A card's Send works once, for 30 minutes, for the draft exactly as shown | Use Edit in Koltrix and review it there |
One consequence deserves a plain statement. If your app supports cards but you cannot see one, the assistant cannot send from that chat, because in an app that supports cards the Send button is the only route. Open the draft from the link the assistant gives you and send it in Koltrix.
Should you care
Cards are a convenience. They make triage faster to scan and make the moment of sending harder to misunderstand, because the whole message and its recipients sit in a box in front of you with a button. If you only draft in Koltrix and send yourself, the draft card is mostly a nicer way to review.
But the design principle is the same as the rest of the integration: the assistant prepares, the person decides. The card is the clearest form of that yet, since the button is yours, not the model's.
Key takeaways
- MCP Apps lets a tool result appear as an interactive card. Apps that do not support it get the same tools as text.
- Koltrix has four cards: mailbox picker, conversation list, conversation and draft review.
- The cards load nothing from the internet and show email content as plain text.
- When sending is on, the Send button on the draft card is the confirmation, backed by a one-time token and every other check.
- If no card appears, nothing is broken. Open the draft in Koltrix. Details are in the docs, and the overview is at koltrix.com/mcp.
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