If you have more than one mail account configured - in my case "Local" and an IMAP account - the "check for mails" button in the symbol bar will open a drop down menu if pressed for some time. In this drop down you can select the account in which to check for mails. The order in which the accounts are listed in this drop down list apparently is random, changes order between kMail restarts and stays stable as long as kMail is running. Reproducible: Always