Unfortunately, you can’t.
If you lose your mailbox.org Guard password, there is no way to retrieve your original PGP key from our server. We at mailbox.org do not store your password on our systems for security reasons and as a consequence, we will not have any backups or copies of your password, or any other mechanism at our disposal to decode or retrieve your key files.
Unless you have an accessible backup, any e-mails or files previously encrypted with the key that is lost can no longer be decrypted. This is not something we invented but the usual consequence in any PGP encryption scenario.
Note that without the Guard password, it is not possible anymore to remove previously added key pairs from your key list!
What to do: Create or upload a new pair of keys
If your Guard password is lost, you can continue using your account by creating a new pair of keys for encryption. You may create the new keys either directly in the mailbox.org interface or alternatively, in a local mail client and then upload them to mailbox.org.
Go to the Guard PGP settings page. In your key list, click on the “+” symbol after the Your Key List headline. A pop-up window will appear, giving you the aforementioned options to choose from. Whether you create a new pair of keys here automatically, or upload them from someplace else, you will then also need to create (and remember!) a new Guard password.
For the new key pair you must then define a new password. Please remember your password well!
You now have two (or more) key pairs in your key list, whereby the last generated or uploaded key pair is automatically marked as "Current". Only the key pair marked as "Current" is used by the mailbox.org-Guard for encryption.
You should then distribute the public key from this key pair to your communication partners and advise them not to use the old key anymore. Data encrypted with the old key cannot be accessed with the new key.
Alternative: let us reset your Guard
To reset the Guard, please create a support ticket in our portal help.mailbox.org with the subject "Please reset Guard". Please note that resetting the Guard will result in the server removing all PGP keys stored in the Guard. If you do not have a local backup copy(s), you will no longer be able to access your e-mails and data encrypted with the old key.
After the Guard has been reset, you can activate it again if you wish.
Note: if you reset the mailbox.org Guard, it will not deactivate your existing inbox encryption.
In this case, make sure that you are still in possession of the corresponding private key!