What you can do to keep your mail from crashing the game.
Opening de mail box will let you see the last 8 mail that came in.

When you now select all en process the mail there is the possibility to click more then once on the green button.
This will 100% crash the game.

If you go to the first mail that came in, scroll down to get there,

Now process the mail, select all, choose destination.
You can click only once on the green button because the mail is instantly processed.

The game will now continue without a hitch.