Version: (using KDE 4.4.3) OS: Linux Installed from: Archlinux Packages If I'll open an external link and then exit from Kmail, kio_imap4 processes remain running until I didn't close my web browser (Firefox).
Looks like not only kio_imap4. All kio_file remains running too.
Thank you for taking the time to file a bug report. KMail2 was released in 2011, and the entire code base went through significant changes. We are currently in the process of porting to Qt5 and KF5. It is unlikely that these bugs are still valid in KMail2. We welcome you to try out KMail 2 with the KDE 4.14 release and give your feedback.