“changed Setup for email@example.com” this message comes very often. Every time the key is changed but even worse the following message in not encrypted. Both use Deltachat. In K9 I can see, that “Empfangsbestätigungen” are send, which are not encrypted. I don´t know why this Empfangsbestätigungen come and how to turn it off.
Unencrypted message is a read receipt. You can disable read receipts in the settings, then your DC will not send and will not request them.
As for “changed setup …” it is probably because your contact uses different keys in different clients. Maybe they have K-9 and Delta Chat, or have installed Delta Chat on desktop and mobile. Ask them to synchronize the keys via “autocrypt setup message”.
Thank you for the fast answer.
As far as I know my contact uses only DC on desktop. I use destop and android mobile version.
I disable the read receipts in the settings. Hope this will solve the problem.
Disabling read receipts can’t help with “changed setup” messages.
If this error continues, it means you contact sends you messages without Autocrypt header or with a different key. In this case makes sense to inspect headers of the last few messages to figure out the problem.
But it seems to solve the problem. I have disabled the “read receipts” in the settings and I do not get the message “Changed setup for. . . . .” up to now. The reason for the problem without disabeling is probably that the E-mail-server interprets the “read receipts” as a “confirmation of receipt” and sends an unencrypted mail. (DC does not show that E-mail, but in K9 it is shown.) This mail interrupts the chain and as a consequence DeltaChat starts again with the key exchange, so it sends the message “Changed setup for. . . . .” So if you have that issue try disable the “read receipts” in the settings.
DC follows Autocrypt standard and ignores unencrypted read receipts when evaluating autocrypt peerstate. Email server should not interpret read receipts in any way too, for server it is just a normal mail.
Maybe one of the servers is outlook? It is known to modify mails. Maybe it can cause such problems by transforming read receipts into normal mails or something like that.