Mailman: Excellent, you're making real progress! I will
have to double my efforts to beat you! Yes, it seems after level 21 things get really tough. I think there are only 30 levels in the game...? Level 24 is really hard, even compared to 23, but there are ways around it. I don't really want to write too many walkthrus for the opposing team; but I will say it's up to you how much ammo you take with you - if you die and end up losing the whole lot then that's up to you.
Will try again soon