Hello there, cski9.
It seems you're unable to see emails older than about a week old for your personal email account on your iPhone 6 Plus. Although it seems you've done some great troubleshooting already, the following Knowledge Base article offers up some steps to review for troubleshooting mail issues:
Get help with Mail on iPhone, iPad, and iPod touch
- Make sure that you're connected to the Internet
- Verify your user name or password. Sign in to your email provider’s website and make sure that your email account is active.
- Check your email settings. If the settings are unavailable, contact your email provider.
- Close and reopen Mail.
- Restart your iOS device.
If you can add an email account to your iPhone, remove the affected email account from your device:
- Tap Settings > Mail, Contacts, Calendars.
- Tap the email account.
- Tap Delete Account.
- Add your account again.
If you have a POP email account, make sure that your email settings match your device.
- Tap Settings > Mail, Contacts, Calendars.
- Tap the email account.
- Make sure that the information matches what you see on your device.
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If you still can’t send or receive email, contact Apple Support.
Thanks for reaching out to Apple Support Communities.
Cheers.