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New: Posteo S/MIME add-on available now

Created on 11. February 2026, 12:30 | Category: Info

Update: The Addon is availabe for Firefox and Chrome

Dear customers,

We have some news: We have released our new, easy-to-use end-to-end encryption with S/MIME in Posteo webmail. From now on, it can be used with the AI-free Firefox alternative, Waterfox. The add-on for Firefox is still waiting to be verified by Mozilla. Support for additional browsers and mobile devices will soon follow (we will then update this post in each case).

You can sign, encrypt and decrypt your emails with S/MIME with the help of the add-on directly in the Posteo webmail interface.
Our Posteo development team has developed its own add-on for this purpose. As of now, the add-on has had two security audits performed by independent security experts (Cure 53). It is now available for download directly in your Posteo account settings and can be used with the Waterfox browser in Windows, macOS and Linux. You can find it in the settings via the menu point “PGP- and S/MIME-encryption”.

#more#

We place a lot value on integrated encryption being accessible for everyday use – and it also being connected seamlessly into the familiar webmail interface. We as a provider do not save your private key on our servers in the process: Your certificates (including private key) remain on your device locally at all times. This is the only way to ensure true and reliable end-to-end encryption.
Users should be able to have full control themselves of the keys for their communication needs – and not have to trust their provider. This contributes to digital self-determination. With our add-on, we want to show that end-to-end encryption can also work easily and seamlessly in the webmail interface without saving keys on a provider’s server.

We have offered inexpensive S/MIME certificates already since 2024 for your Posteo address(es). They can be acquired with ease in your account settings with just one click (365 cents per year) and they can be used immediately. For a long time, creating certificates for private users was comparatively complicated and cost-intensive even though S/MIME contributes significantly to secure email communication, regardless of provider.
S/MIME is already natively supported in virtually all email clients (also on mobile devices). By being able to also use S/MIME securely with Posteo webmail we want to reach everyone who loves our webmail interface as much as we do.

The plug-in imports the certificates of your communication partners automatically as soon as you click on an S/MIME-signed email. Additionally, it searches for published certificates in the Posteo key directory and uses them automatically when writing to someone whose certificate you do not yet have. Keys are also searched using S/MIMEA.

Here’s what S/MIME can do

S/MIME is a globally used standard for end-to-end encryption and for signing emails that is already integrated in many email clients and apps like Outlook, Thunderbird or Apple Mail. S/MIME certificates issued by a certificate authority are displayed as trustworthy in these programs. This is how you can tell if an email actually originates from the respective sending address. Only you need a certificate for signing your emails: For encryption, your communication partners must also use S/MIME.

By the way, our add-on can not only be used with S/MIME certificates aquired at Posteo, you can also use certificates obtained elsewhere with us.

At Posteo, S/MIME signatures are also checked and the result of the check is displayed in the webmail interface and web app without using the add-on. In the meantime, quite a few large companies and some authorities are signing their emails with S/MIME so that you can recognize the authenticity of an email at a glance.

You can learn how to install and use the S/MIME add-on in our help section:
https://posteo.de/en/help/end-to-end-encryption-with-smime-in-posteo-webmail-interface

Best regards,
The Posteo Team

New: Posteo doubles storage space to 4 GB

Created on 04. February 2026, 10:00 | Category: Info

Dear Posteo customers,

We have good news: Starting immediately, the price of €1 per month includes more storage space – we are increasing it from 2 GB to 4 GB.

The adjustment applies to all Posteo mailboxes: both for new and existing customers.
The storage usage bar has already been adjusted accordingly. If a lower percentage of occupied space is displayed, don’t worry: nothing has been deleted. Your storage space has simply been increased.
#more#

If you have booked additional storage space, you will no longer pay the surcharge for the first 2 GB (€ 0.25/month per GB) in future.
The monthly fees for mailboxes have already been adjusted; you do not need to do anything.

Why we can offer more storage space for 1 EUR

This upgrade has also been made possible by you – or rather, by our new Cleanup Tool, which we introduced six months ago.
With this new feature, you can clean up your mailbox and free up used storage space with just a few clicks.
The Cleanup Tool has been very well received. So well, in fact, that we can now offer more storage space at no extra charge.
We had been thinking about this for a long time, and it was one of the reasons we introduced the new Cleanup Tool last June.

We would like to thank all Posteo customers who are already using the Cleanup Tool.

Use the Cleanup Tool and free up storage space

Even though it’s still a little early for the annual spring cleaning, we would like to take this opportunity to promote the Cleanup Tool once again. You can find it under “Attachments.”
Select it, and all the files in your mailbox will be displayed in a clear list. The largest files are shown at the top, with smaller ones further down.
You can filter the overview by file types such as PDF files, images, presentations, spreadsheets, text files, and folders.

Often, deleting just a few of the largest attachments in your mailbox is enough to free up enough storage space for a long time to come. The best part is that you can keep the corresponding emails and download the attachments with a single click before deleting them, if necessary.

If you delete an attachment from an email, a brief note is automatically inserted into the corresponding email. It contains the name of the deleted file and the date of deletion. This allows you to see that the email originally contained an attachment. You can, of course, also delete the entire email.

You no longer need to spend time cleaning up your mailbox or purchasing additional storage space. This saves you time and money. And it also helps protect the environment, as less data is stored online.

Best regards,
Your Posteo team

New at Posteo: The Cleanup Tool for email attachments

Created on 19. June 2025, 14:00 | Category: Info

Dear Posteo customers,

We have released a new feature: Our Cleanup Tool. Now you can tidy up your email account more efficiently and free up storage space quickly.

#more#

The Cleanup Tool in Posteo webmail.
Attachments are sorted by size. In the upper-right, you can see the occupied storage space

Maybe it has happened to you before: You wanted to reduce the storage space used in your email account and deleted a lot of emails but barely any storage space was freed up. This is because most emails are very small in size. It’s common for only a few large messages with file attachments to occupy a lot of storage space.

With the Cleanup Tool, you can quickly identify what is eating up your storage space. You can immediately see which attachments are using a lot of storage space. It is often sufficient to delete a few of the largest attachments in your account to have enough storage space available again for a long time. The highlight: You can keep the associated emails – and, if needed, you can download attachments before deleting.

With the new Cleanup Tool, you no longer need to laboriously search through your email account for large emails or book more storage space. This saves you time and money. It also helps the environment if less data is stored online.

All attachments in a compact overview

You can find the Cleanup Tool via “Attachments”. When selecting it, all attachments will be prepared in a clearly structured list. The largest attachments will be displayed at the top and the smallest further below.

It is also possible on smartphones to quickly free up storage space using the Cleanup Tool.
The Cleanup Tool by Posteo

Additionally, the overview allows you to filter by file types such as PDF files, images, presentations, spreadsheets or text files.

You can also only display attachments found in individual folders.

You can now quickly and easily delete attachments to free up storage space.
If an attachment is deleted from an email, the Cleanup Tool will automatically insert a brief note to the associated email. This note contains the name of the deleted file as well as the date of deletion. This way, you can remember that the email originally contained an attachment. If you also no longer need the email, of course you can also delete the entire email.
Furthermore, you can download the files before deleting them with just one click.

The new Cleanup Tool is available to you at no additional cost. It expands on the attachment browser with our integrated photo stream which you can also find in Posteo webmail via “Attachments”.

Privacy notice: New features are always designed by us so that no personal data is collected in the background. This reinforces your right to informational self-determination. The Cleanup Tool is developed solely by Posteo without any third parties involved. The preparation of attachments in a list view only occurs upon your request – and the results are only temporarily stored locally in your browser. We do not store this information on our servers and it is also not passed on.

Best regards,
Your Posteo Team

How to use app passwords with Posteo

Created on 07. March 2025, 17:00 | Category: Info

Dear Posteo customers,

Do you manage your emails in external clients like Thunderbird, Outlook or Apple Mail? If so, you can use app passwords for this purpose.
With application-specific passwords, email clients on your device can access your Posteo emails with their own, separate password. For example, one password can be used for an email app on your mobile phone and another password can be used for an email client on your computer.

#more#

App passwords can be created and deleted in your Posteo account settings
App passwords can be created and deleted in your Posteo account settings

You can create and manage app passwords in “Settings” via “Password and security”.
These passwords typically only need to be entered once in the respective application. You will not be prompted to enter it again each time you open the application. If a device is lost, stolen or is otherwise compromised, you can simply delete an app password in the settings of your Posteo account. By doing so, you can intentionally prevent any potential unauthorized access without needing to change your email account’s password and then update it in multiple programs as the case may be.

You can also complement app passwords with two-factor authentication: This secures access via the Posteo website and our web app with an additional one-time password. Two-factor authentication also protects access to your Posteo account settings as these are only available via the webmail interface.
Do you only want email clients and devices to be able to access your emails if an app password is used? If so, then activate additional email account protection. This blocks external applications from accessing emails using the Posteo password.

Application passwords can also be used in combination with crypto mail storage, a feature that encrypts all your emails with your passwords.

App passwords are an optional feature for external applications – such as email clients and email apps.
If you exclusively use Posteo via our web login or the Posteo web app, this feature has no relevance for you. Tip: For optimal protection, activate two-factor authentication and additional email account protection.

You can learn how to use app passwords in our help section: https://posteo.de/en/help/app-passwords

Best regards,
Your Posteo Team

New security certificate

Created on 17. February 2025, 20:00 | Category: Info

Dear Posteo customers,

We are updating our main security certificate. Security certificates are only valid for a specified time period and need to be renewed from time to time.

In most cases, you will not notice any change.
All current clients like Thunderbird or Outlook will automatically find the new certificate. You do not need to do anything. However, should your client display a certificate error during this changeover process, please restart your client. This should fix the error.
#more#
If you manage the trustworthiness of certificates manually, you can find the fingerprint for the new main certificate below. You can also find complete fingerprints for all certificates in our legal notice.

New fingerprint for the TLS security certificate for posteo.de:

Geotrust:
SHA256: 64:59:9B:20:CD:28:CE:58:6A:C4:3C:F5:E8:84:AD:9D:28:8A:29:CB:44:AF:D4:79:EB:C2:47:8B:D6:86:C6:05
SHA1: 72:7C:16:4D:38:1E:44:C2:BB:A7:56:98:E3:27:9B:B4:3E:CE:65:B9

Best regards,
The Posteo Team