iphone 4 mail not automatically updating

In my experience, it won't be updated until a new message received is pushed from the server or until the account is automatically checked for new messages in the background if Push access is not enabled for the account.

I get this problem with my Yahoo (Rogers) account. Even though Push is enabled for the account, it doesn't automatically update unless I open the mail app. What's worst, old emails linger on my iPhone even though I've since deleted them on my computer. The only way to make it disappear on the iPhone is by emptying the inbox. I remember when I first got my iPhone 4, this was not a problem. But in the last month or so, this problem popped up.

Did you create the account on your iPhone using the Yahoo account preset?

If so, the account was created as an IMAP account with Push access for received messages. If not, you are accessing the account as a POP account and Push access is not supported with a POP account and POP account mailboxes are not kept synchronized with the server.

If you are accessing your Yahoo account as an IMAP account on the iPhone, you are not accessing the account as an IMAP account with the email client used on your computer for accessing the account. Yahoo does not support accessing a Yahoo account as an IMAP account anywhere except with the iPhone's Mail app.

Accessing an account as a POP account with an email client on your computer and as an IMAP account with another email client is a recipe for potential problems.