Version: (using Devel) Installed from: Compiled sources The tab line takes valuable vertical space, and clutters the UI. The "New Tab" button could be placed at left of the search line when there is no tabs.
If I understand correctly, there is a setting for this in the message list setup (hide tab bar when only one tab is open). Problem: When this setting is active, the button for opening a new tab also disappears. So you can't use tabs at all.
There are no menu entries to handle the tabs in kmail 1.10.92, and only a few users will search the shortkey for that action.
Yes, we need to change the default. This however requires a bit more changes, since it needs a "Open in new tab" in the folder context menu then. And for that, it needs to be able to show the context menu without selecting the folder, which means all the actions of the context menu have to be changed to be able to operate on non-open folders. It's on my todo list.
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.