mailbox (formerly mailbox.org) vs Posteo

Compare mailbox (formerly mailbox.org) and Posteo on capabilities, jurisdiction, assurance, and fit for European buyers.

Both listed as alternatives to: Gmail

mailbox (formerly mailbox.org)

Germany· Office Productivity Suite

Needs review

Shortlist mailbox when you need a German-operated email-plus-collaboration suite (Mail, Drive, Office, Meet, Admin/API) on dual Berlin sites with published BSI C5 Type 1 and ISO 27001 claims. Skip when you require free forever mail or default zero-knowledge for all messages—consider Proton Mail or Tuta instead.

German-operatedBerlin dual-site hostingPGP + S/MIMEBSI C5 Type 1 (claimed)ISO 27001 (claimed)Mail + Drive + Meet + Office

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Posteo

Germany· Email Services

Needs review

Shortlist when you want a paid German mailbox on self-operated servers, open protocols (IMAP/CalDAV), and extreme data minimisation (no inventory data, unlinked payments). Skip when you need custom domains, default E2EE without setup, multi-seat enterprise admin, or an Art. 28 DPA—consider Proton Mail, Tuta, mailbox.org, or Mailfence instead.

Self-operated DE serversData-minimising signupIMAP / CalDAV / CardDAVBSI TR-03108 (verified)Optional crypto mail storageAd-free, user-funded

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Highlighted rows differ between the two products.

mailbox (formerly mailbox.org) vs Posteo: Snapshot
Feature	mailbox (formerly mailbox.org)	Posteo
Country of origin	Germany	Germany
Category	Office Productivity Suite	Email Services
Open source	No	Yes
Self-hosted	No	No
Headquarters	Germany	Germany
Legal entity	Heinlein Hosting GmbH (Berlin; CEO Peer Heinlein)	Posteo e.K., Methfesselstr. 38, 10965 Berlin
Governing law	Not listed	German / EU law (GDPR, BDSG, telecom secrecy / TTDSG as applicable)
US parent / control	No known US parent	No known US parent
CLOUD Act exposure (indicative)	Low	Low
Hosting / residency	Core mailbox, Drive, and Meet on Heinlein-operated servers in German data centres in Berlin (two independent locations). Website analytics: self-hosted Matomo. Marketing site may embed Vimeo/YouTube. No public AWS/GCP/Azure product hosting region found for customer mail data.	Self-operated infrastructure; stored mail and backups in Germany (Frankfurt, Bielefeld, Berlin DCs per privacy materials). No AWS/GCP/Azure listed for mailbox hosting. Payment top-ups may use PayPal/card networks (unlinked from accounts per Posteo).
Summary	German paid digital workplace from Heinlein Hosting GmbH: secure email with PGP/S/MIME, Drive, browser Office, Meet, and business Admin on dual Berlin data centres.	Independent Berlin email provider with self-operated German servers, data-minimising signup, open-standard clients, and layered optional encryption—not a free-tier ad network.
Tags	email privacy gdpr productivity german-hosting bsi-c5 iso-27001 collaboration	email privacy gdpr open-source encryption green-energy germany

At a glance: mailbox (formerly mailbox.org) vs Posteo
At a glance	mailbox (formerly mailbox.org)	Posteo
HQ	Berlin, Germany	Berlin, Germany
Legal entity	Heinlein Hosting GmbH	Posteo e.K. (HRA 47592 B)
Hosting	Own servers, dual independent Berlin sites	Self-operated servers in Germany
Model	Paid subscription SaaS; trial available; no permanent free tier	Not listed
Self-host	No (managed SaaS)	No (hosted service)
Open standards	IMAP/SMTP, CalDAV/CardDAV, WebDAV, PGP, S/MIME	Not listed
Commercial model	Not listed	Prepaid paid service; no free tier
Protocols	Not listed	IMAP, POP3, SMTP, CalDAV, CardDAV
Founded	Not listed	2009
Energy	Not listed	100% green energy (Green Planet Energy, claimed)

Key capabilities: mailbox (formerly mailbox.org) vs Posteo
Key capabilities	mailbox (formerly mailbox.org)	Posteo
German-operated	Yes	Not listed
Berlin dual-site hosting	Yes	Not listed
PGP + S/MIME	Yes	Not listed
BSI C5 Type 1 (claimed)	Yes	Not listed
ISO 27001 (claimed)	Yes	Not listed
Mail + Drive + Meet + Office	Yes	Not listed
Self-operated DE servers	Not listed	Yes
Data-minimising signup	Not listed	Yes
IMAP / CalDAV / CardDAV	Not listed	Yes
BSI TR-03108 (verified)	Not listed	Yes
Optional crypto mail storage	Not listed	Yes
Ad-free, user-funded	Not listed	Yes

mailbox (formerly mailbox.org)

PGP Guard, S/MIME, and hardened mail transport
Webmail Guard for PGP without extra software (or Mailvelope with local keys), S/MIME for sign/encrypt, 2FA and app passwords, multi-stage spam/virus rejection, plus public transport controls (DNSSEC, DANE, MTA-STS, DMARC/DKIM/SPF, TLS checker, @secure.mailbox.org aliases). Benefits security-minded teams that still need interoperable IMAP/SMTP; content is not zero-knowledge by default unless you encrypt.
Drive on dual independent Berlin sites
Cloud files on the provider's own German infrastructure with two independent Berlin locations, WebDAV, mobile apps, guest share links, expandable quota, and optional client-side OpenPGP encryption of stored files. Fits teams replacing consumer cloud drives while keeping residency claims concrete; confirm plan quotas on the official site.
Browser Office with CalDAV and CardDAV
Edit common office formats in the browser, share calendars and contacts via open CalDAV/CardDAV standards, plus tasks, notes, polls, and TLS-secured XMPP chat. Aimed at SMEs and schools that want collaboration without a full Microsoft desktop stack; advanced Excel macros and deep Office add-ins are not the target.
Meet video hosted in German data centres
Browser-based conferencing integrated with calendar and mail: link invites for external guests, breakout rooms, screen share, chat, surveys, and moderator controls. Privacy documentation references the OpenTalk stack; sessions run through mailbox's German data centres. Evaluate E2EE defaults and recording policies against your meeting compliance needs.
Business Admin console and automation API
Central management of domains, mailboxes, quotas, spam/virus settings, IP allowlists, and backups, with an HTTP API for larger orgs and resellers (api.mailbox.org). Supports onboarding help and partner-assisted migration. Better for multi-seat German operations than pure consumer inboxes; not a full IdP replacement without SSO design work.

Posteo

Signup without identity data; payments unlinked
Accounts can be created without name, address, or phone. Posteo's payment system (bank transfer codes, cash, card, PayPal) is designed so payment identifiers are not stored against the mailbox. Practical limit: recovery options you add yourself and how you fund the prepaid balance still affect anonymity in the real world.
Optional crypto mail storage for the whole mailbox
One setting encrypts stored messages—including metadata—with a key protected by the account password (RSA/AES/HMAC/bcrypt design; Dovecot plugin). Posteo states it cannot disable crypto storage once enabled and cites a Cure53 review. Limit: this is server-side encryption at rest after delivery, not sender-to-recipient E2EE, and losing the password can mean losing access to encrypted data.
TLS, DANE, and BSI-certified secure transport
Access is TLS-only with PFS, HSTS, and DANE/TLSA. Optional TLS-sending/receiving guarantees refuse delivery over cleartext peer links. Posteo holds BSI TR-03108 v2 Secure Email Transport certification (BSI-K-TR-0745-2025). Transport quality still depends on the remote provider's stack.
CalDAV/CardDAV with optional password encryption
Calendars and contacts sync via open standards and can be AES-encrypted in Posteo's database so the provider cannot read them when the feature is on. Trade-off: encrypted calendars cannot be shared the same way, and password reset without the old secret can lock you out of encrypted PIM data.
In-house migration without third-party movers
Posteo's own migration tool pulls mail (and often contacts/calendars) over encrypted links from previous providers without routing through a third-party migration SaaS. Quota: a limited number of migrations per account, with an optional collector for ongoing fetch from the old box.

Assurance & compliance: mailbox (formerly mailbox.org) vs Posteo
Assurance & compliance	mailbox (formerly mailbox.org)	Posteo
Independent security / no-logs audit	Not found No public independent no-logs audit PDF found; operational transparency reports and BSI/ISO artefacts instead	Partial BfDI on-site privacy inspection (2016) confirmed data-minimisation / no inventory IP model (public PDF). Crypto mail storage: vendor cites Cure53 multi-level audit; full public report not located. Not a continuous independent no-logs certification programme.
ISO 27001	Vendor claimed Vendor states ISO/IEC 27001:2022 on certified-quality and press pages; request current certificate in diligence	Not found No ISO 27001 claim found on primary Posteo security/privacy pages.
SOC 2 / SOC 3	Not found No SOC 2/3 claim found on primary security/cert pages	Not found No SOC 2/3 report advertised on primary pages.
BSI C5	Vendor claimed Vendor press (7 Jan 2026): BSI C5 Type 1 attestation for mailbox; confirm type, scope, and period	Not listed
GDPR / EU data protection	Vendor claimed German controller Heinlein Hosting GmbH; DE hosting; detailed privacy notice; DPO privacy@mailbox.org	Vendor claimed German entity; privacy policy cites GDPR/BDSG/telecom secrecy; DPO published; BfDI inspection history.
US CLOUD Act exposure (indicative)	Partial EU/German entity, no known US parent, self-operated Berlin hosting for core data—no AWS/GCP/Azure product region found. Residual: marketing embeds (Vimeo/YouTube) and possible external payment services. Indicative assessment only, not legal advice.	Partial EuropeanStack assessment: German e.K., no known US parent, self-operated DE hosting with no public US-cloud mailbox subprocessors → indicative exposure low. Status is partial (not a clean bill): payment rails and lawful German disclosure remain. Not legal advice.
Data processing agreement (B2B)	Vendor claimed Business knowledge base: customers can conclude a DPA online; historic AVV portal for business accounts	Not found Vendor states it is not an Art. 28 processor as a public electronic communications service and does not offer customer DPAs.
EU AI Act	Not applicable Email/collaboration suite, not an AI product core	Not applicable Conventional email/PIM service; not an AI product.
BSI TR-03108 Secure Email Transport	Not listed	Verified BSI certificate BSI-K-TR-0745-2025 (OpenSource Security GmbH audit; valid through 2030 per BSI listing).

Considerations & known limitations: mailbox (formerly mailbox.org) vs Posteo
Considerations & known limitations	mailbox (formerly mailbox.org)	Posteo
Mail is not zero-knowledge by default	Medium Without PGP/S/MIME, stored message content remains operator-accessible under legal process. Practical impact: train users or mandate Guard/S/MIME for confidential traffic.	Not listed
C5 Type 1 is point-in-time	Low Type 1 attestations describe design/implementation at a point in time. Re-check type (1 vs 2), scope, and renewal dates for public-sector RFPs.	Not listed
Payment and edge processors need confirmation	Low Core hosting is self-operated DE, but privacy text references external payment services; marketing embeds US video hosts. Ask for the current processor list with the DPA.	Not listed
Not a full Microsoft 365 ecosystem substitute	Medium Browser Office and Meet cover common collaboration; deep desktop macros, Graph automations, and third-party M365 marketplaces will not map 1:1.	Not listed
No customer self-host option	Low Organisations that must operate mail on their own iron need another stack; mailbox is multi-tenant SaaS.	Not listed
No custom domains	Not listed	High Posteo will not host your own domain. Organisations needing brand continuity or provider portability via DNS must pick another host or self-host.
Encryption is layered, not default E2EE	Not listed	Medium Without crypto mail storage, inbound encryption, or client-side PGP/S/MIME, Posteo can process mailbox content like a normal provider. Lawful intercept (TKU) and seizures remain possible under German process; transparency reports show content releases do occur under court order.
No customer Art. 28 DPA	Not listed	Medium Procurement checklists that require a signed processor agreement will stall. Posteo argues telecom special law applies instead; validate with legal counsel for your use case.
Password loss risk with crypto features	Not listed	Medium Crypto mail storage and encrypted calendars/contacts depend on the account password; Posteo cannot recover plaintext if that secret is lost after encryption is enabled.
Payment processors outside pure DE mail path	Not listed	Low Optional PayPal/card top-ups involve non-German commercial processors even though Posteo says it does not link payment identity to the mailbox. Cash/bank-code paths reduce that linkage further.

Fit

mailbox (formerly mailbox.org)

Best fit when

German or EU orgs replacing Gmail/Microsoft 365 for mail and light collaboration under German law
Teams that need IMAP/SMTP plus CalDAV/CardDAV and optional custom domains
Buyers that will use PGP Guard or S/MIME deliberately for sensitive mail
SMEs and schools wanting Drive, browser Office, and Meet without a US hyperscaler
Organisations that need multi-seat Admin, DPA, and an automation API

Poor fit when

Users who need a permanent free tier
Buyers requiring default zero-knowledge mail for every user without crypto setup
Teams that must self-host the full stack on their own infrastructure
Enterprises whose workflows depend on deep Microsoft Graph or Google Workspace add-ons

Consider instead when

When: You need default end-to-end encrypted mail as the primary product
Consider: Proton Mail or Tuta
Stronger E2EE-first posture; lighter full workplace suite than mailbox
When: You want minimal German privacy email without Drive/Office/Meet
Consider: Posteo
Leaner mailbox; fewer collaboration modules
When: You need full desktop Office parity and global SaaS integrations
Consider: Microsoft 365 (incumbent) with separate residency controls
Different risk and ecosystem tradeoff—not an EU peer

Posteo

Best fit when

Individuals and small teams who want German jurisdiction and open-standard clients without Google or Microsoft mail
Users prioritising anonymous or low-identity signup and prepaid funding without linking payments to the mailbox
Organisations that accept posteo.* addresses and value no ads, no tracking, and published transparency reports
Operators who want optional full-mailbox encryption at rest (crypto mail storage) plus PGP/S/MIME tooling
Buyers who need BSI-aligned secure email transport certification rather than US SOC 2 paperwork

Poor fit when

Anyone requiring custom domains or branded organisational addresses
Teams that need default zero-access E2EE for every message without enabling optional layers
Procurement processes that mandate a signed Art. 28 DPA, SOC 2, or ISO 27001 from the vendor
Large enterprises needing multi-seat admin, shared domain policies, or deep Microsoft/Google workspace integration

Consider instead when

When: You need default end-to-end encryption and a broader encrypted suite
Consider: Proton Mail or Tuta
Posteo is IMAP-first with optional crypto layers; Proton/Tuta lead with zero-access defaults.
When: You need custom domains or richer business mail hosting
Consider: mailbox.org or Mailfence
Posteo deliberately refuses own domains to avoid inventory-data obligations.
When: You need free-tier consumer mail tightly integrated with docs and chat
Consider: Gmail or Outlook.com
Trade privacy posture and EU self-operation for ecosystem convenience.

Open questions for due diligence

mailbox (formerly mailbox.org)

What is the exact current BSI C5 scope, type, and validity period on the attestation document?
Which payment processors and any other subprocessors appear in the live AVV annex?
What is the default Meet encryption mode (TLS-only vs optional E2EE) for your plan, and is recording available?
Which SSO/IdP integrations are supported for your business tier beyond generic SSO mentions?

Posteo

Does your counsel accept Posteo's position that no Art. 28 DPA is required for occupational use?
Will posteo.de / .net / .com addresses meet your brand, deliverability, and anti-spoofing requirements without custom domains?
Which encryption layers (crypto mail storage, inbound PGP/S/MIME, client E2EE) will your users actually enable and support?
Do you need ISO 27001/SOC 2 artefacts that Posteo does not publish?
Is BSI TR-03108 transport certification sufficient for your sector's secure-email checklist?