circleback vs Email Inbox API + Sending by Sendmux
circleback is a plugin bundle for AI coding tools published by circlebackai. Marketplaces we read that list it: 2 (Claude Code: claude-plugins-official, Claude Code: claude-plugins-community). Email Inbox API + Sending by Sendmux is an MCP server published by Sendmux. Marketplaces we read that list it: 1 (Official MCP Registry). As of our marketplace pass on 2026-10-14. This pair was picked by a reader, not by our comparison rule, so search engines are asked not to index the page.
Where each is published
| Marketplace |  circleback |  Email Inbox API + Sending by Sendmux |
|---|---|---|
| Claude Code: claude-plugins-official | Listed Version: 1.0.0 Forks (GitHub): 5 Stars (GitHub): 3 Not marked · First seen |
Not listed |
| Claude Code: claude-plugins-community | Listed Version: 1.0.0 Forks (GitHub): 5 Stars (GitHub): 3 Not marked · First seen |
Not listed |
| Official MCP Registry | Not listed | Listed Version: 2.2.0 Downloads/month (npm): 398 Downloads/week (npm): 46 Forks (GitHub): 1 Stars (GitHub): 65 Not marked · First seen |
Each figure is the marketplace's own and is never added up across marketplaces. A marketplace that publishes no figure shows none: no number is not zero.
The facts side by side
| Fact | circleback | Email Inbox API + Sending by Sendmux |
|---|---|---|
| Marketplaces that list it (differs) | 2 (better) | 1 (worse) |
| Stars (GitHub) (differs) | 3 (worse) | 65 (better) |
| Forks (GitHub) (differs) | 5 (better) | 1 (worse) |
| Last release | Not published | Not published |
| Where it runs (differs) | Remote server (circleback.ai/api/mcp) | Remote server (mcp.sendmux.ai/mcp) |
| Transport | Streamable HTTP | Streamable HTTP |
| Tools it declares | Not published | Not published |
| Environment variables it asks for (differs) | Not published | 4, secrets among them: 3 |
| Parts of the bundle (differs) | 1 | Not a bundle |
| Licence | Not stated | Not stated |
| Repository (differs) | github.com/circlebackai/claude-code-plugin | github.com/sendmux/sendmux-sdk |
| Changes in the last 7 days | 0 | 0 |
| First seen | 2026-10-11 | 2026-10-11 |
| Endpoint at the last check | not checked yet | not checked yet |
Lines where the two differ have a tinted background and bold values. Where the data itself says which value is better (more marketplaces, a larger figure of the same marketplace, a fresher release, a verified mark on a marketplace that lists both), the better one is also marked green with ▲ and the worse one red with ▼. Where it runs, the transport, the tools, the settings, hooks, the bundle's parts, the licence and the week's changes are marked only as different: more or fewer is not better in itself.
What each says it does
circleback
Circleback conversational context integration. Search and access meetings, emails, calendar events, and more.
Email Inbox API + Sending by Sendmux
AI email inbox and sending tools with attachments, search, live events, and webhooks.
How to run each
circleback As a Claude Code plugin
/plugin install circleback@claude-plugins-officialEmail Inbox API + Sending by Sendmux As a remote MCP server
claude mcp add --transport http sendmux-mcp https://mcp.sendmux.ai/mcpRequires: SENDMUX_MAILBOX_API_KEY (secret), SENDMUX_MANAGEMENT_API_KEY (secret), SENDMUX_MCP_SURFACES, SENDMUX_SENDING_API_KEY (secret)
Commands built only from what the marketplaces declare; the full set for every client is on each card.
Tools each declares
Neither one's marketplaces publish a list of tools, so there is nothing to compare.
Settings each asks for
The marketplaces of circleback publish no settings it asks for, so we do not compare settings.
What it can do: circleback · What it can do: Email Inbox API + Sending by Sendmux · Compare two other plugins
Data comes from the public marketplace file https://github.com/anthropics/claude-plugins-official/blob/HEAD/.claude-plugin/marketplace.json. Data comes from the public marketplace file https://github.com/anthropics/claude-plugins-community/blob/HEAD/.claude-plugin/marketplace.json. Data comes from the Official MCP Registry (registry.modelcontextprotocol.io), CC0 1.0. Figures come from our own regular passes over the marketplaces, last read on . We publish no contact details for plugin publishers.