You can store your database on mailbox.org. Read on for details.
Setup
In Strongbox, tap Add or Create and choose WebDAV from the list of options. When asked enter the details below:
WebDAV URL
The WebDAV URL is generally of the form:
https://office.mailbox.org/servlet/webdav.infostore/Userstore/Firstname%20Lastname.
NB: The first and last name at the end of the URL separated by %20. This the name which users use in their "profile", and it is accessible via the profile image on the mail screen, top right. See our screenshot below:
So, for example the WebDAV URL example above would become:
WebDAV URL for John Doe: https://office.mailbox.org/servlet/webdav.infostore/Userstore/John%20Doe
Username & Password
The username/password for Mailbox.org WebDAV has to be generated using an Application specific password:
Settings > Security > Application Passwords:
one can create a new App Specific password for Strongbox:
There you can create a password and it will automatically create a new username (even though it is only labelled as "Add new password"). It will look something like this:
In Strongbox then, once you have entered the above, you can browse for an existing file stored on Mailbox.org or select a folder to create a new database in.
Warning: Login 2.0 - 2FA Preview
If you have enabled the new beta "Login 2.0" or "2FA preview" the above steps may not work at all. A workaround is to disable the new beta Login 2.0, then create the new app specific username/password and then re-enable Login 2.0 again.
Mailbox.org Support
Mailbox.org have a very helpful user forum at https://userforum-en.mailbox.org. All questions are best addressed there as we are not Mailbox.org experts.