When users want to setup their second device, even with the new “Add second device” feature, most users click on the first button they see (“login to your email account”). This leads to many issues; users should be guided away from it.
Expected behavior
When users login to an email account, and we detect that they used Delta Chat in the past, there should be a pop-up prompting them to “add as second device instead”. There should be additional options to either import a backup or continue with logging in/creating a new PGP keypair if they lost all other devices with Delta Chat installed.
Actual behavior
The user enters their password to login, a second PGP keypair is created, old messages are not shown, incoming messages can’t be decrypted, …
There are different ways how we could detect whether a user has used Delta Chat in the past:
Check whether an IMAP folder called “DeltaChat” exists
Check if there are outgoing e-mails in the account with a Chat-Version header
We could also store a signed e-mail to self in the DeltaChat folder which indicates that a client exists, including relevant metadata about it. This way, different clients could know about each other.
