The latest software update for Apple's iPhone could change the way Google's Gmail works on the handset.

In an advisory notice published to the Google Gmail Help Center, Google warns users who configured Gmail access on their iPhone by tapping the Gmail icon in Mail set-up will see the mail service automatically updated to enable IMAP mail services once the iPhone update is installed.

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"This means that actions you take on your iPhone will now sync with actions in your Gmail web interface (i.e. messages you read on your iPhone will show up as 'Read' in the web interface). This also means that messages you delete on your iPhone will be moved to the Trash folder in the Gmail web interface, and thus deleted after 30 days," the company warns.

"Please exercise caution when deleting messages, as this behaviour is markedly different from POP access." The company also offers users the information they need to continue using IMAP without deleting messages, and instructions to return the iPhone to using POP access.