GuideUpdated October 30, 2026

Keep Posteo or mailbox.org and use an AI email agent

If your mail lives at Posteo or mailbox.org, you can still work with an AI agent without switching providers. The agent either signs in to your mailbox over IMAP and SMTP[5][11], or it works on a copy that your provider forwards to an inbox built for agents[4][10]. Each route adds someone who can read your mail, so pick it on purpose.

Command Mail is our product, and it is one way to do the forwarding route. This guide walks through it and also covers direct IMAP access, which some people who chose a privacy-focused provider will prefer. We start with where your data ends up.

Updated: Fact-checked: About 11 min readAs Markdown

Contents
  1. The short version
  2. Where your data goes
  3. Before you start
  4. Step 1: Add the address in Command Mail
  5. Step 2a: Forward from Posteo
  6. Step 2b: Forward from mailbox.org
  7. Step 3: Send from your real address
  8. Step 4: Connect your agent with few permissions
  9. The direct route over IMAP
  10. Check that it works
  11. Common problems
  12. Next steps
  13. Sources and date
  14. Frequently asked questions
  15. Sources

01The short version

  1. Decide whether your agent gets a forwarded copy or direct IMAP access.
  2. For a copy: add the address in Command Mail under Settings → Connect mailbox, then forward to its private intake address, at Posteo under Settings → My account → Forwarding[4] and at mailbox.org under All settings → Read and write e-mail → Rules[10].
  3. On Pro, create an app password and add it under Settings → Connections in Command Mail if replies should come from your real address.
  4. Connect your agent with narrow permissions and widen them once you trust its work.

02Where your data goes

People pick these providers for a reason. Posteo lists servers in a German data centre on its features page[9], and mailbox.org says it runs its services only in data centres in Berlin[15]. If your agent uses an AI model run by another company, that company joins in and processes whatever the agent reads under its own terms. Only a locally run model keeps this step on your machine; Thunderbird MCP explicitly lists local models as an option[18].

Forwarding to Command Mail adds another operator. Command Mail is run by FYN Labs LLC in the United States, the app and database run on Cloudflare, Inc., also in the US, and attachments are stored in Cloudflare's EU jurisdiction[3]. The privacy policy bases transfers to the US on the EU-US Data Privacy Framework where the recipient is certified, and on standard contractual clauses otherwise[3].

For spam and phishing checks, sender, recipient, subject, attachment names and up to 4,000 characters of text from incoming mail go to the provider TypeSafe[3]. According to our app code, this also includes the sender's display name and, if you set up automatic labels, their names and sorting instructions; the code does not specifically strip card numbers beforehand.

Two web app features send more to TypeSafe, again according to the app code. Opening the agent panel on a received message sends sender and display name, recipient, the redacted subject and up to 4,000 characters of text; opening the list of similar messages sends the original message plus up to 30 candidates, each with sender, subject and up to 1,000 characters of text. Our page on AI email assistant privacy lists the exact fields.

Direct IMAP access creates no copy at another hosted service. Local programs still keep their own data on your computer: mcp-email-server keeps an SQLite database for mailbox listings and can write large responses to temporary files[16], and Thunderbird can keep folders available offline[18]. The program your agent runs also holds an app password for your mailbox[6][12]. IMAP has no approval step of its own, so whatever that password can do, the program can do.

Forwarded copy (Command Mail)Direct IMAP (local MCP server)
Where mail is storedOriginal at your provider, copy at Command MailAt your provider; local copies and caches on your computer are possible[16][18]
What the agent holdsA Command Mail sign-in with the permissions you choseAn app password for your mailbox
SendingOn Pro, via SMTP with an app password or via relay; approval per draft available[2]Via your provider's SMTP[5][11]; limits depend on the program
Encrypted mailboxPosteo: mail that arrived unencrypted is forwarded readable unless a filter encrypts it[7]; mailbox.org: copy stays encrypted[10]The program must be able to decrypt and must allow the agent to read encrypted mail[18]
EffortSet up forwarding, install nothingInstall and maintain a program

03Before you start

For the forwarding route you need a Command Mail account. Free covers receiving, reading, sorting and drafts in one mailbox and shows the last 90 days. Sending and up to ten mailboxes come with Pro, which the plan overview lists at €19 per month for the first 100 paying Pro accounts, as long as that subscription runs, and €29 per month after that[2].

You also need access to your Posteo or mailbox.org settings and, if you want to send, the option to create an app password there[6][12]. The agent comes last: anything that speaks MCP, such as Claude, ChatGPT or Codex.

04Step 1: Add the address in Command Mail

Add your address in Command Mail, either under Settings → Connect mailbox or on the command line with commandmail mailboxes connect me@posteo.de. Command Mail then shows the private intake address your provider should forward to[1]. Keep it at hand for the next step.

05Step 2a: Forward from Posteo

In Posteo, open Settings, click My account, open Forwarding and click Add new forwarding. Enter the intake address from step 1 and save[4].

Posteo's help lists three details worth knowing. New mail always lands in your Posteo inbox too, so there is no forwarding without a copy. You can forward to up to five addresses. Mail in the Posteo spam folder and mail that arrives through an email collector is not forwarded[4].

If you pull other accounts into Posteo with the collector, their mail will not reach Command Mail[4]. Connect those addresses on their own instead.

If you use inbound encryption, Posteo encrypts new mail in your inbox with your public key. Forwarded mail is not encrypted with your key, mail that is already encrypted is not encrypted again, and the help adds that you can use filters if you want forwarded mail encrypted too[7]. Without such a filter, mail that arrived unencrypted reaches Command Mail in readable form while the original sits encrypted in your inbox; mail the sender already encrypted stays encrypted.

06Step 2b: Forward from mailbox.org

In mailbox Office, go to All settings → Read and write e-mail → Rules and click Auto forward. Enter the intake address, choose whether copies stay in your inbox and confirm[10]. Keep the copies while you test.

To forward only part of your mail, add a new rule there instead. Set the condition, for example one sender, choose Redirect to as the action, enter the intake address, turn off the check against subsequent rules and save[10]. The agent then sees only the mail that matches the condition.

The encrypted mailbox changes the picture. mailbox.org's knowledge base says mail is forwarded in encrypted form when the encrypted mailbox is active[10], and only someone with your private PGP key and its password can read it[14]. Command Mail does not decrypt PGP, so an agent would see ciphertext and could neither summarize nor sort sensibly. With the encrypted mailbox on, forwarding is not a workable agent route.

07Step 3: Send from your real address

On Pro you set up replies from your Posteo or mailbox.org address per address in Command Mail under Settings → Connections[1]. Only a person in the app can do this; an agent cannot create a sending route. You can complete the setup on Free, but nothing goes out before Pro.

According to the app code, Command Mail prefills posteo.de on port 465 for posteo.de and posteo.net addresses, and smtp.mailbox.org on port 465 for mailbox.org addresses. Both providers document port 465 with TLS or 587 with STARTTLS for outgoing mail[5][11]. Command Mail signs in to the server before saving the route and stores the password encrypted.

Posteo. Create an app password under Settings → My account → Password and security → App passwords (device passwords) → Create app password. Enter a description, confirm with your Posteo password and click Create app password now[6]. It needs at least 16 characters, including a digit and an uppercase letter, and you can have up to five at once; Posteo shows it only once[6].

As the user name, Posteo expects your account login, usually the address you chose when you signed up; you can look it up in the overview under My account[5]. Command Mail prefills the connected address, so change the field if you connected an alias. If your login ends in posteo.com, posteo.at or another Posteo domain, the help says the server is still posteo.de[5]; type it yourself, because the prefill only recognizes posteo.de and posteo.net.

With additional email account protection turned on, SMTP works only with an app password[8], which is what this route uses anyway.

mailbox.org. In mailbox Office, open All settings → Security → Email app-passwords, name the password, select the allowed protocols and generate it[12]. SMTP is enough for Command Mail. Once two-factor authentication is on, external programs can no longer sign in with your normal password, so you need an app password regardless[13].

mailbox.org always expects your main email address as the user name[11]. If you connected an alias or an address on your custom domain, which the pricing page lists from the Standard plan up[15], change the prefilled user name accordingly and enter smtp.mailbox.org with port 465 or 587 by hand.

If you would rather not store a password, use the Command Mail relay. You confirm your address with a code, and Command Mail sends from its own address with Reply-To set to yours. Recipients then do not see your own address as the sender.

08Step 4: Connect your agent with few permissions

Connect your agent over MCP, for example in Claude Code with claude mcp add --transport http commandmail https://commandmail.app/mcp[2]. You pick permissions when you sign in. To start, mail:read for reading and sorting and mail:draft for drafts that never send are enough[2]. mail:send-approved sends exactly the draft revision you approved, and mail:send allows sending without approval from mailboxes on auto[2].

Keep in mind that mail:read reads every mailbox on your account. The autonomy level per mailbox controls what the agent may change there; it does not separate access. New mailboxes start on suggest, or on read if that is your account default. See Permissions and autonomy for the details.

09The direct route over IMAP

If you want no copy at another hosted service, point a local MCP server at your provider's IMAP and SMTP servers. Posteo uses posteo.de for both, with IMAP on port 993 over TLS[5]; mailbox.org uses imap.mailbox.org on port 993 and smtp.mailbox.org[11]. Create a separate app password for it, so you can revoke it later without changing your main password[6].

Two open-source options. mcp-email-server (BSD-3 license) reads, searches, organizes and sends over IMAP and SMTP. It has five write classes, namely draft, organize, delete, send and append, and an empty list makes an account read-only[16]. You can restrict sending to a list of allowed recipients, and an empty list turns sending off[17].

Thunderbird MCP (MIT license) runs as an extension inside Thunderbird, listens on localhost by default and opens a review window before sending by default[18]. It only hands encrypted mail to the agent after you turn on "Allow MCP clients to read encrypted messages" in its options and Thunderbird has your key set up[18].

mailbox.org gives you one extra lever here: each app password has its own protocol selection[12]. A password limited to IMAP cannot send over SMTP. IMAP still allows moving and deleting, so this only guards against unwanted sending. For the broader trade-offs, see IMAP MCP vs hosted MCP.

10Check that it works

Send a test message from another account to the forwarded address. It should show up in your original inbox and in Command Mail shortly after. Then ask your agent for your newest mail; it should name the test message by subject and sender.

To test sending, reply to the test account and look at the sender there. With SMTP you see your real address, with the relay you see the Command Mail address and your address in Reply-To. We have not checked whether the reply also appears in your provider's Sent folder.

11Common problems

Some messages never arrive. Posteo does not forward spam or mail from its email collector[4]. Check the Posteo spam folder, and connect collected accounts to Command Mail directly.

The agent only sees encrypted content. The mailbox.org encrypted mailbox is on and forwards encrypted copies[10]. Decide whether you need it for this address, or use the direct route with a program that has your key set up and allows the agent to read encrypted mail[18].

The SMTP sign-in fails. Check that you entered an app password instead of your main password and that user name, server and port are right. At mailbox.org, the password must allow SMTP and the user name is your main address[11][12]; at Posteo, the server is always posteo.de[5]. Command Mail accepts only ports 465 and 587.

Messages arrive twice. Check whether several rules forward the same message to the same intake address, for example Auto forward plus an extra rule at mailbox.org[10]. Keep one.

12Next steps

Start with one address, keep a copy at your provider and give your agent read and draft permissions for the first week. To bring addresses from several providers together, follow All your addresses in one inbox.

Start Command Mail for free, forward your address and connect your agent.

13Sources and date

Last checked: 2026-10-30. All provider pages and the public Command Mail pages were retrieved that day. Statements about the prefilled outgoing servers, the sign-in test, encrypted password storage, the relay and that only a person can create a sending route also rest on the app code at commit d9ab36c (smtp-presets.ts, send-routes.ts, SendingSetup.svelte); that code contains no PGP decryption. This guide does not claim a hands-on run with real accounts.

Frequently asked questions

Does Posteo or mailbox.org have its own connector for ChatGPT or Claude?

We found no connector or MCP server on the help, feature and pricing pages we read. An agent reaches these mailboxes over IMAP and SMTP with an app password, for example through a local MCP server, or works on a forwarded copy in an inbox built for agents.

Do my emails stay at Posteo when I forward them?

Yes. Posteo's help says new mail is always delivered to your Posteo inbox as well. Forwarding adds a copy at the destination, and archiving or deleting that copy does not touch the original.

Can an agent read mail from an encrypted mailbox?

At Posteo, inbound encryption does not apply to forwarded mail unless you set up a filter for it, so mail that arrived unencrypted is forwarded readable. mailbox.org forwards mail from its encrypted mailbox in encrypted form. Command Mail does not decrypt PGP, so an agent would only see ciphertext.

Can I reply as me@posteo.de from Command Mail?

Yes, on Pro. For posteo.de and posteo.net addresses Command Mail fills in the server posteo.de on port 465, and you add an app password. mailbox.org addresses get smtp.mailbox.org. Command Mail tests the login before it saves the route.

Which route shares less data?

Direct IMAP access creates no second copy at another company, but the program your agent uses holds an app password, and local programs keep their own copies and caches. If your agent uses a model run by another company, that company processes whatever the agent reads in both cases.

Sources

  1. Command Mail: Documentation, forwarding, import and sending commandmail.app, accessed
  2. Command Mail: Plans and agent permissions commandmail.app, accessed
  3. Command Mail: Privacy policy (last updated 2026-10-28) commandmail.app, accessed
  4. Posteo Help: How do I set up email forwarding? posteo.de, accessed
  5. Posteo Help: Setting up Posteo in an email client (POP3, IMAP and SMTP) posteo.de, accessed
  6. Posteo Help: What are app passwords and how do I use them? posteo.de, accessed
  7. Posteo Help: Inbound encryption with your public PGP key posteo.de, accessed
  8. Posteo Help: Activating additional email account protection posteo.de, accessed
  9. Posteo: Features posteo.de, accessed
  10. mailbox.org Knowledge Base: Forward emails automatically kb.mailbox.org, accessed
  11. mailbox.org Knowledge Base: Email configuration kb.mailbox.org, accessed
  12. mailbox.org Knowledge Base: Email app-passwords kb.mailbox.org, accessed
  13. mailbox.org Knowledge Base: Access security, 2FA and app passwords kb.mailbox.org, accessed
  14. mailbox.org Knowledge Base: Your encrypted mailbox kb.mailbox.org, accessed
  15. mailbox.org: Prices and plans mailbox.org, accessed
  16. mcp-email-server: Tools and write classes github.com, accessed
  17. mcp-email-server: Configuration and allowed recipients github.com, accessed
  18. Thunderbird MCP (TKasperczyk): README github.com, accessed
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