New install, cannot send, cannot connect to encryption service?

After a new install (ver 5.600 on android 10 / lineageOS) and with all previous email settings reloaded, I cannot send email anymore. The German error message is “Verbindung zu Verschlüsselungsdienst fehlgeschlagen” (failed to connect to encryption service).

  • I do not want to use encryption because I do not want to store my keys on the mobile device.
  • I do not have open keychain installed
  • I do not find the option “disable encryption”
    The lock on the top-right of a new message is red and the errormessage is also shown when I tip the lock.
    I am surprised that I find nothing on google or this forum. Am I the only one?

Help appreciated. Karl