kmail 4.18 stays in offline mode, unable to send emails

It just happened to me that I couldn't send emails with kmail. There was no error, no warning. Sending emails just resulted in nothing happening. Mails stayed in the out box. I toggled on and off the Online Mode, to no avail. I had to reboot the computer and everything went back to normal.

https://bugs.kde.org/show_bug.cgi?id=294441
Version: 4.8
says it's fixed. Apparently not.

There is talk about the Mail Dispatcher agent being offline. I don't know what it is nor where to find its status.

See also:
https://bbs.archlinux.org/viewtopic.php?id=135361
https://bbs.archlinux.org/viewtopic.php?id=135284