Connect mailbox.org to Sickle

mailbox.org works with any IMAP mail app. Sign in with your main mailbox.org address and your password — or, if you use two-factor authentication, an email app password made for Sickle. You can create one without two-factor too, to give Sickle its own password that you can delete on its own.

Add the mailbox once, on the web or in the Mac app, and it shows up in both — and in every agent you have connected to Sickle.

Before you start

• A Sickle account. If you do not have one yet, start a free trial.
• Your main mailbox.org address, such as [email protected]. Mail apps sign in with it, not with an alias.

Create an email app password

You need this if two-factor authentication is on; mailbox.org then refuses your normal password in mail apps. Without two-factor it is optional.

1. In mailbox.org, open Settings, then mailbox.org → Email App-Passwords.
2. Enter Sickle as the name.
3. Allow both IMAP and SMTP.
4. Click Generate Password and copy it.

mailbox.org's own instructions are in Creating email app passwords and E-mail configuration.

mailbox.org's server settings

• IMAP server — imap.mailbox.org, port 993, SSL/TLS.
• SMTP server — smtp.mailbox.org, port 465, SSL/TLS (or 587 with STARTTLS). The Mac app sends the mail you write through it, and so does your agent when you approve a send.

Connect on the web

1. Sign in at sickle.app and open Mailboxes.
2. Click Connect mailbox and choose Other.
3. Enter your main mailbox.org address and your password (or the email app password). For IMAP server enter imap.mailbox.org and port 993; for SMTP server, smtp.mailbox.org and port 465.
4. Click Connect. Sickle signs in to mailbox.org to check everything before it saves; you see Checking… while it does.

Connect in the Mac app

1. Click + at the bottom of the sidebar (Add mailbox). On first launch, the onboarding screen shows the same choices.
2. Choose Manual authorisation (⌘7).
3. Enter your main mailbox.org address. Under Inbox settings (IMAP), enter the password, imap.mailbox.org and port 993; under Outbox settings (SMTP), the same password with smtp.mailbox.org and port 465.
4. Click Sign in.

Check it worked

The mailbox appears in the list on the Mailboxes page. If you have an agent connected, ask it "Which mailboxes can you see?" — the new one is there, with nothing to reconnect.

Troubleshooting

• "Authentication failed" or "The mail server rejected these credentials". Check you used your main address, not an alias. If two-factor authentication is on, your normal password will not work — use an email app password.
• Reading works but sending fails. The app password allows only IMAP. Create a new one with both IMAP and SMTP allowed.
• It worked, then stopped. You turned on two-factor authentication, or the app password was deleted. Create a new one and enter it in the Can't sign in notice in the Mac app.

Disconnect

On the Mailboxes page, click Disconnect next to the mailbox. If you created an app password for Sickle, delete it under Settings → mailbox.org → Email App-Passwords too.

Next: connect your agent

Your mailbox.org account is ready for any agent you connect to Sickle. Pick yours: Claude, Claude Code, Codex, Cursor or OpenClaw.