Can't move email messages to trash?

Try a Reset [Hold the Home and Sleep/Wake buttons down together for 10 seconds or so (until the Apple logo appears) and then release. The screen will go blank and then power ON again in the normal way.] It is app and data safe!

What happens when you try ? If you are getting a 'cannot be moved to trash' message then try going into Settings > Mail, Contacts, Calendars > select the account > account name , tap on SMTP (under the 'Outgoing Mail Server' heading) and then tap on your Primary Server and try entering your email account and password and see if it then works