Did you try changing the delete settings for emails for that account? Touch the account in the Accounts section of the Settings > Mail, Contacts, Calendars screen, and then touch Advanced at the bottom of the account's settings screen.
You can then set Mailbox Behaviors: In the Mailbox Behaviors section of the Advanced settings screen, choose
** Drafts Mailbox to set whether drafts are stored on your iPhone, or remotely on your email server.
** Deleted Mailbox to set whether deleted messages are immediately trashed or saved remotely on your email server.
You can also set:
* Deleted Messages: Decide when deleted messages should be removed permanently from your iPhone. Touch Remove and then choose a time. Your options are Never, After One Day, After One Week, or After One Month.
I hope this helps.