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Troubleshooting
The authorization screen says this needs Skybox Pro
Connecting an assistant, like API keys, is part of Skybox Pro. The screen shows this before anything is selected and sends you back to the assistant without connecting. Upgrade to Pro (see skyboxmail.de/pricing) and connect again.
The connector shows as disconnected, or every request fails with "sign in again"
The connection was revoked: under Settings → Connected Apps in Skybox, by removing the connector on another device, or because your Skybox account was deactivated. Connect it again through the assistant's connector settings. Nothing in Skybox needs to change first.
The assistant says an account or folder does not exist
Most likely the account is not in the connection's account selection. Open Settings → Connected Apps, choose the connection and Account Access, and tick the account. The next request sees it.
If the account is selected, the assistant may have mixed up coordinates: a message is identified by account, folder and a number within that folder, and a search spans several accounts. Ask it to search again; it then picks the message up with the right coordinates.
The assistant says the mail account is locked
Skybox locks a mail, calendar or contacts account when its provider rejects the stored credentials repeatedly, for example after a password change or an expired OAuth grant. Open the account in Skybox and re-enter the password or reconnect it; the assistant works again as soon as Skybox can.
Sending or uploading a file fails
For attachments the assistant uploads the file from its own workspace to Skybox over HTTPS. Some assistant environments restrict outgoing connections; the host that has to be reachable is api.skyboxmail.de (or your Enterprise instance). An attachment is limited to 25 MB; a larger file is offered as a download link instead, which the assistant can choose when it uploads.
If the instance has no file storage enabled, the upload tools are not offered at all, and the assistant can attach only files that already exist in a mailbox, by referring to them.
A move or delete seems stuck
Moves, copies, deletions and flag changes run as background jobs. The assistant waits around 20 seconds and otherwise reports the job as still running; it can check on it with get_mail_job. A job survives a restart of Skybox and finishes on its own. In Skybox the affected folders update as the job progresses.
Claude Code cannot connect
Make sure the server was added with the HTTP transport:
sh
claude mcp remove skybox
claude mcp add --transport http skybox https://api.skyboxmail.de/mcpThe first request opens the authorization screen in your browser.
Still stuck
Write to hello@skyboxmail.de with the time of the failing request and, if the assistant showed one, the error text. Skybox logs every tool call by name, so the time is enough to find it; the message content is never in the logs.