Q: email folders have  not dowloaded

Hey Duncan1Wtg,

Thanks for asking your question in the Apple Communities. Congratulations on your new iPhone 6s! 

To get your Yahoo mail folders downloaded to the new device, you would not need to delete the account in the old device. The folders will download if the Yahoo mail account is an IMAP or an Exchange account, and these folders must be seen from Yahoo. If you go to Safari or any internet browser, go to Yahoo.com. Log in and see if those folders are listed in the webmail. If they are not shown in your webmail, then they will not sync to the new device.

If they are shown online, please turn the phone off, and then turn the phone back on. Restart your iPhone, iPad, or iPod touch See if the folders start downloading then.

If they do not, verify this account is an IMAP account. You can do that by entering in your email address into this settings link to check: Mail Settings Lookup

As long as it is an IMAP account, and you see those folders at Yahoo.com, the folders should come through. I recommend removing the account, and reading it. Add an email account to your iPhone, iPad, or iPod touch

If you still have trouble, you can check this article: Get help with Mail on your iPhone, iPad, and iPod touch

Hope these help get your mail in order on your new phone.

Cheers.