Hi, I've set up kmail ( actually Kontact but behaviour is the same) with two mail accounts. I also have two identities wich use different smtp accounts. If i reply to a mail in second account or compose a new mail while second account is selected, the identitie for the first account is selected by default. How can I change that, so that when replying or composing a mail in second account, the second identitie is selected?

I think you can select the preferred identity per mail resource, if you use different resources (different IMAP servers, etc.), it's hidden in the "advanced" configuration tab of the IMAP resource, at least. Alternatively this can be set per-folder in the folder properties dialog (right click on a folder and select "Properties").