Spam by the game! (White Giant)

I returned to my nation to see that I had received over 300 messages in one day because I had set the game to auto sell shares of my public corporations. This is not acceptable I have spent ages deleting them. How do I turn off the setting that sends me all of these irrelevant messages and if there isn't one then this problem seriously needs to be fixed!

There is a check box to enable/disable automatic messages of share sales/purchases.

You can also scroll down and toggle selection to mark all and then mass delete.

At the time I did not have the setting to message me about share transactions entered manually turned on, is there another setting? Secondly there is a button called (un)mark all but I see no button to mark all, is that the same button or is there another?

It is the same. It marks all messages that were not marked and unmarks any that were marked.