When deleting e-mails, I don't want to accidentally mark the next e-mail as read. One easy way to improve this is to mark the deleted e-mail's line blank and change the text to "deleted" instead of deleting it from the list and selecting the next e-mail.
Also, since sometimes I don't want to mark my very last or first email as read in my account, you need to display a blank entry at the beginning and end of every folder's message list. This allows the user to click that spot and avoid accidentally marking their messages as read, when they haven't gotten around to them.
This also prevents users from accidentally deleting alot of messages by fat-fingering the delete key. This also cat-proofs your e-mail app. Jesus, so many reasons to do this, so few not to.
This is basic sanitation stuff.