While some users prefer the convenience of sending messages to new contacts immediately, even if they are unencrypted, users with higher security requirements find unencrypted communication unacceptable.
It looks like the possibility of including encryption keys in the QR code will still take time:
Therefore I suggest a simple short term solution: include a setting which, when enabled, will include an extra bit in the QR code or invite link to instruct the app on the scanning device to prohibit sending messages until end-to-end encrytion is established.
This way, users who prefer the convenenience of sending unencrypted messages immediately can still do so, while users with higher security requirements won’t need to worry that new contacts will send them unencrypted messages.
If this option is enabled, Delta Chat on the device used to scan the QR code could display a message such as “Chat request sent. You will be notified when this contact approves the chat request” and then display a notification when E2EE is established.
Expected behavior
There is an option to prevent unencrypted communication with new contacts
Actual behavior
There is no option to prevent unencrypted communication with new contacts