You will only see notifications for the first three email accounts created + messaging on the lock screen. If you want a different email account to show, delete one (or more) of the first three created which will shift the accounts around. Then you can recreate the account you deleted, but it won't show anymore.
Why is it every single day I find more and more things like this that shouldn't be!
More and more limitations to the WP7 OS.. Come on MS, get with the program already!
I really do want to like WP7, but MS needs to step it up.. they are the largest software company on the planet and they can't get little things like this correct. What would be so hard to show all email account notifications? It's not like there's a lack of screen real-estate..
My problem is I have to turn the screen on, type my passcode and check. It's not the biggest issue in the world but battery life is important. Not having an LED notification for emails and only displaying 3 icons means wasted time checking.. I'm spoiled by Android and comparing it.. =/
I understand your concerns, especially regarding battery life. Not trying to judge here but do you really have more than three important email accounts that require constant monitoring. I had as many as 5 accounts on my device at one point but since deleted 2 to clear space on my Start screen. If some accounts only drop an occasional message would it not be ok to check them less often, like when you have other reasons to unlock you device. Its like Marketplace. No notification on the lock screen, but its not like I must have that update, even though some times I am waiting for one in particular. I may be way off base but figured I would throw it out there anyway.