IPhone syncing protocols rely on several email credentials, such as your username, password, and correct server settings. If these elements are typed incorrectly or changed, then your iPhone might not be able to sync email. You can resolve this issue by updating your email credentials and resyncing your Mail app.
Updating Your Settings
Launch the Settings app on your iPhone and tap, "Mail, Contacts, Calendars." Choose the email address you wish to update. Make sure that your email address is typed correctly, and then tap "Account." Update the "Password" field with your current email password. Tap "Advanced" to review your incoming mail settings. Some email services, such as Gmail, automatically fill in these fields for you. Check with your email administrator for any additional credentials you might need, such as outgoing mail servers and SSL ports.
Resync your Inbox
Launch the mail app and choose your updated email account from the "Mailboxes" menu. Once the Inbox loads, swipe downward to resync your email account. New messages that you have received appear in the inbox.
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