Status: The lettron.eu mail service is in development and not yet available. The "lettron.eu (planned)" row describes our plans; all other rows describe existing services. Information as of 5 October 2026; later changes by the providers are not reflected.
This page sets four features of our planned mail service beside what existing providers state about the same features. It is meant to help you place the planned approach and is not a rating. What is said here about other providers comes from their own websites, help pages and legal texts; the references are listed under "Sources".
Four features at a glance
Where the provider is based
| Provider | Statement |
|---|---|
| Proton Mail | Switzerland (Proton AG, Plan-les-Ouates, Geneva) |
| Tuta Mail | Germany (Tutao GmbH, Hanover) |
| mailbox.org | Germany (Heinlein Hosting GmbH, Berlin) |
| Posteo | Germany (Posteo e.K., Berlin) |
| Gmail | For users in the EEA and Switzerland: Ireland (Google Ireland Limited). According to Google, it belongs to the group of companies of Google LLC, USA. |
| Outlook.com | For users in the EU: Ireland (contracting entity Microsoft Ireland Operations Limited). The German imprint of microsoft.com names Microsoft Corporation, USA, as the provider. |
| lettron.eu (planned) | Germany (patchletter UG (haftungsbeschränkt), Gelsenkirchen; operator of this website) |
Access with common mail apps (IMAP, SMTP)
| Provider | Statement |
|---|---|
| Proton Mail | Through the additional Proton Mail Bridge software for macOS, Windows and Linux, only with a paid Proton Mail plan. Business plans also offer SMTP sending for applications and devices. |
| Tuta Mail | Not supported. Tuta states that it does not offer IMAP, POP3 or SMTP and points to its own apps and to add-ons for Thunderbird. |
| mailbox.org | Native. IMAP and POP3 in the Light, Standard and Premium plans; sending over SMTP. |
| Posteo | Native: IMAP, POP3 and SMTP |
| Gmail | Native. According to Google, IMAP access is always turned on for personal Google Accounts. |
| Outlook.com | Native. According to Microsoft, POP and IMAP access is disabled by default and can be enabled in the settings. |
| lettron.eu (planned) | Planned: native (IMAP, SMTP) in the default Compatible mode, in all plans |
Your own domain
| Provider | Statement |
|---|---|
| Proton Mail | Yes, with a paid plan |
| Tuta Mail | Yes, in all paid subscriptions; not in the Free plan |
| mailbox.org | Yes. Standard and Premium plans for private customers (Light only within family accounts) and Business accounts. |
| Posteo | No |
| Gmail | With Google Workspace from the Business Starter plan. Google's plan comparison for Gmail lists "Custom domain" only for the paid plan. |
| Outlook.com | According to Microsoft, Microsoft 365 Personal or Family subscribers have not been able to create a new address with a personalised domain for their Outlook.com mailbox since 30 November 2023; existing ones continue to work. Microsoft points to its Microsoft 365 Business plans. |
| lettron.eu (planned) | Planned: from the Pro plan |
Stored mail the provider cannot read (by its own account)
| Provider | Statement |
|---|---|
| Proton Mail | Default ("zero-access encryption"). According to Proton, nobody else can access messages and attachments in the inbox, not even Proton. Subject lines and sender and recipient addresses are, according to Proton, encrypted but not end-to-end encrypted. |
| Tuta Mail | Default. According to Tuta, all user data is stored end-to-end encrypted and the decryption key is available only to the user. Metadata such as sender and recipient addresses is excepted. |
| mailbox.org | Option ("PGP-encrypted inbox"). According to mailbox.org, only people with the private PGP key and the corresponding password can then access newly arriving messages. |
| Posteo | Option ("crypto mail storage"). According to Posteo, the encrypted data is then no longer readable by the provider either; it is decrypted only at the moment of access. |
| Gmail | Option in certain Workspace editions (client-side encryption). According to Google, Google servers and third parties cannot decrypt it; subject, timestamps and recipients are not additionally encrypted. Otherwise Google refers to "default encryption". |
| Outlook.com | No statement. For Microsoft 365 Personal or Family subscribers, Microsoft describes an option to encrypt individual messages. |
| lettron.eu (planned) | Planned as an option per folder ("Sealed", OpenPGP). In the planned default ("Compatible"), mail is stored encrypted, but the server processes plain text while you are logged in. |
We reproduce what the providers write about themselves; we have not tested the services technically. "No statement" means that, on the date above, we found no unambiguous statement by the provider on this point in the sources listed below. It says nothing about the service itself.
The lettron.eu details are plans and may change before launch. More is on the Security, Mail apps and open standards, Your own domain and Pricing pages; the Roadmap shows the planned order.
What the tables do not show
Four features do not describe a mail service in full, and we chose them. Storage, calendars, ease of use and support do not appear here; we leave out prices because they change often. Each of the services named has strengths that are missing from the tables. A few examples from the providers' own information:
- Proton Mail: apps for the web, iOS, Android, macOS, Windows and Linux. According to Proton, all its apps are open source and have been independently audited by third-party experts.
- Tuta Mail: its own apps for the web, Android, iOS, Linux, macOS and Windows; all clients are published under the GPLv3 licence. According to Tuta, calendars and contacts are encrypted by default as well.
- mailbox.org: celebrated its tenth anniversary in 2024, by its own account, and refers to a BSI C5 certificate and ISO 27001 certification. Depending on the plan, the service also includes Drive storage, Office and video conferencing.
- Posteo: established in 2009, by its own account. According to Posteo, its crypto mail storage underwent an external security audit in 2014; Posteo also refers to a certification under the technical guideline on secure email transport of the German Federal Office for Information Security (BSI).
- Gmail: according to Google, available on computer, phone, watch and tablet, including at no cost, and connected with Google Meet, Google Calendar and Google Chat.
- Outlook.com: can be used with the new Outlook, with Outlook for Mac and with the Outlook mobile app. According to Microsoft, Microsoft 365 subscribers get additional features.
The features are connected. Tuta gives its end-to-end encryption as the reason for not offering IMAP, and with Proton the Bridge encrypts and decrypts mail on your own computer. Our planned default mode takes the other route: common mail apps are meant to work without additional software, and in return the server processes plain text during a session. For content that we should not be able to read, the Sealed mode is intended; it will launch only after an external cryptography audit. An ordinary mail app will not open Sealed folders directly. We describe the limits of both modes on the Security and Mail apps and open standards pages.
You can use all the services named today. You cannot yet use lettron.eu: the mail service is in development, and audits and penetration tests are still to come before launch.
Sources
What is said about the other providers is based on the following pages of those providers. The addresses are given as text because this website does not link to other sites.
Proton Mail
Retrieved on 5 October 2026.
https://proton.me/legal/terms
https://proton.me/support/imap-smtp-and-pop3-setup
https://proton.me/support/custom-domain
https://proton.me/support/proton-mail-encryption-explained
https://proton.me/mail/download
https://proton.me/community/open-source
Tuta Mail
Retrieved on 5 October 2026.
https://tuta.com/imprint
https://tuta.com/security
https://tuta.com/pricing
https://tuta.com/support#imap
https://tuta.com/support#custom-domain
https://tuta.com/support#open-source
mailbox.org
Retrieved on 5 October 2026.
https://mailbox.org/en/legal-information/
https://mailbox.org/en/prices/
https://mailbox.org/en/about-us/
https://kb.mailbox.org/en/private/faq/compatible-web-browsers/
https://kb.mailbox.org/en/private/custom-domains/using-emails-with-a-custom-domain/
https://kb.mailbox.org/en/business/custom-domains/using-emails-with-a-custom-domain/
https://kb.mailbox.org/en/private/encryption/your-encrypted-mailbox/
Posteo
Retrieved on 5 October 2026.
https://posteo.de/en/site/legal_notice
https://posteo.de/en/site/features
https://posteo.de/en/help/how-do-i-set-up-posteo-in-an-email-client-pop3-imap-and-smtp
https://posteo.de/en/site/faq
https://posteo.de/en/site/encryption
https://posteo.de/site/leistungen
https://posteo.de/site/verschluesselung
Gmail
Retrieved on 5 October 2026.
https://policies.google.com/terms?hl=en&gl=de
https://policies.google.com/terms?hl=en&gl=us
https://support.google.com/mail/answer/7126229?hl=en
https://support.google.com/mail/answer/7104828?hl=en
https://workspace.google.com/intl/en/products/gmail/
https://workspace.google.com/pricing?hl=en
https://knowledge.workspace.google.com/admin/security/about-client-side-encryption?hl=en
https://support.google.com/mail/answer/13317990?hl=en
Outlook.com
Retrieved on 5 October 2026.
https://www.microsoft.com/en-gb/servicesagreement
https://www.microsoft.com/de-de/rechtliche-hinweise/impressum
https://support.microsoft.com/en-us/outlook/pop-imap-and-smtp-settings-for-outlook-com
https://support.microsoft.com/en-us/onedrive/changes-to-microsoft-365-email-features-and-storage
https://support.microsoft.com/en-us/outlook/send-encrypted-messages-with-a-microsoft-365-personal-or-family-subscription
https://support.microsoft.com/en-us/outlook/premium-features-in-outlook-com-for-microsoft-365-subscribers
Reporting errors
If anything on this page is wrong or out of date, please write to the contact address in the imprint.