Allow to delete many message items at once

[sjvudp]

When trying to send a larger text via clipboard to myself (using the mobile app), the text was split into multiple rather short messages (support said it's the way it should be).
Now when I want to get rid of those many messages, both the mobile app, and the web frontend only allow to select one message and delete one message.
It would be nice being able to mark multiple messages (like a range, and being able to unselect a few in between), and then delete them all with one action. That would save a lot of time, and it's not rocket-science at all!
BTW: In the web frontend "select all" does a very odd thing: It selects everything visible in the window (messages displayed AND all contacts)... I have no ioea where this could be useful.