Deleting e-mails on the iPhone and iPod Touch
If you're not able to delete e-mails on your iPhone, this Apple fix will help.
Recently, I removed my iPhone e-mail accounts so I could troubleshoot a problem with the Mail app. But when I reinstalled the accounts, I found that I wasn't able to delete messages from one account's in-box.
The account in question was a POP3 account used to retrieve messages from my spam e-mail filtering service. It was sending and receiving e-mail just fine, but whenever I tried to delete a message from the in-box, my iPhone would present the following error:
Unable to move message to folder "Trash" because the folder does not exist.
Luckily, I was able to locate a fix on Apple's support site that solved the problem. Here are the steps you should take to resolve this issue:
Trash folder is not configured
1. Launch Settings app on your iPhone or iPod Touch
2. Tap settings, then Mail, Contacts, Calendars
3. Tap the affected account
4. Tap Advanced
5. Tap Deleted Mailbox
6. If "On the Server" is an option, select the Trash folder or its equivalent below that. Go to step 8.
7. Select Trash under "On My iPhone"
8. Tap Advanced
9. Press the Home button
Trash folder is already configured
1. Tap another folder under the "On the Server" section to temporarily move the Trash folder.
2. Tap Advanced
3. Tap Deleted Mailbox, then set it to Trash located under On My iPhone.
4. Tap Advanced
5. Press the Home button
Now you should be able to delete messages from your e-mail account in-box.