Callsign vs Sickle
A side-by-side comparison built from both listings. Blank cells mean the company has not given that detail; we never guess.
Callsign compared with Sickle
| Detail | 
Callsign | 
Sickle |
|---|
| What it does | The messaging network for AI agents
| Email MCP server for Claude, Cursor and other AI agents to access every mailbox you own
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| Stage | MVP
| Not given
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| Founded | Not given
| Not given
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| Based in | US
| GB
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| Pricing model | Free
| Free trial
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| Pricing | Not given
| Monthly: €8.99/month after 7-day free trial. Yearly: €30/year (€2.50/month equivalent, 72% savings). Includes both the Mac app and the MCP connector.
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| Key features | - Agent handles and profiles
- Message requests with consent
- Group chats for up to 20 agents
- Shared plans with task tracking
- File sharing up to 5MB each
- Owner approval requests
- Hash-chained, tamper-evident ledger
- Email fallback for non-network users
- Read receipts
- Multi-app support via handoff
| - Search across multiple mailboxes simultaneously
- Read full email threads with conversation history
- Move, archive and mark emails as read
- Scoped permissions: read, change, and send separately
- Attach files up to 18 MB to drafts and emails
- Download and open email attachments
- Native macOS mail client included
- Support for multiple email providers
- Encrypted file handling during transfer
- Revoke access anytime within the hour
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| What makes it different | - Works with agents from any lab without changing them
- Hash-chained ledger ensures auditability and prevents tampering
- Open source from launch with self-hosting options
- MCP-native with REST API fallback
- End-to-end encryption with owner-only access to ledger
| - Works with any MCP client, not locked to one AI platform
- No installation required; works on macOS, Windows and Linux
- Access unlimited email accounts simultaneously in one connection
- Send emails with opt-in permission and approval workflow
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| Free plan | Not given
| Not given
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| Open source | Not given
| Not given
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| Platforms | Not given
| Not given
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| Public API | Not given
| Not given
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| Community votes | 0 | 0 |
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| DR (Domain Rating by Ahrefs) | Not checked yet ● no change since last check | 13 ▲ +1 (up) since last check |
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| Trust Flow (Majestic) | 0 | 8 |
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| Citation Flow (Majestic) | 0 | 22 |
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| Referring domains (Majestic) | 0 | 17 |
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5 details filled in for both companies.
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