I don't know about the receiving email problem. Tell us what kind of account it is and maybe someone can make a bette guess. But I'll guess at some cure all solutions that might work, but shouldn't hurt anything if they don't.
Since you keep all your email on the server, you can always turn off the account and then turn it back on after it disappears from the Mail app. Just go to the account in settings and turn off the switch next to mail. Go to to the Mail app to make sure the account has disappeared, then back and turn it on again. I've done this several times when my calendar gets a bit wonky; usually because I'm playing sync games with other servers.
More drastically you can remove and then re-add the account. As long as you are syncing with an online service your stuff should come right back.
If you are not familiar with how email works since the last update you may not know that you can choose to view just inboxes, including a new universal inbox, or accounts. Hit the back button at the top of the list to go to Mailboxes. If you choose one of the inboxes, that is all you see. If you choose from the account section you will see all the mail folders that are setup to sync from your that account. This usually includes at least the Trash and Sent folders.
