Transferred to new BT Mail from BT Yahoo mail problems

My lady friend has been transferred from BT Yahoo Mail to the new BT Mail, contacts and inbox has transferred without a hitch BUT the personal folders have been transferred BUT cannot expand to view the saved emails in them! Can anyone help on how to view the saved emails in the personal folders?

Is this an Outlook question?

IMAP or POP3?

No, this has happened when the BT Yahoo Mail on the web mail page has been changed to the new BT Mail! The saved email in the personal folders cannot be accessed even as the folders have been transferred. I click to view the emails in the folders and nothing happens, the folders seem to be empty

Checked with various browsers

Thanks for the suggestion, I've only tried it with IE 11. I shall try in the next day or two with other browsers and possibly install Mozilla Thunderbird to see if that makes a difference as she does not have Outlook.

Assume you are
1) Using BT.com to access email
2) You registered for Yahoo email, in April, to be included with BT
3) Your PC has latest Updates installed

My Yahoo email works fine, including boxes, on Windows 7 with IE11 and Firefox.

I

You have assumed correctly she too has Windows 7 with IE11
1) Using BT.com to access email
2) The BT Yahoo Mail has now transferred to new BT Mail, as was asked when she logged into the BT Yahoo Mail as usual
3) PC has all latest updates as they are set to automatically update

It is very odd as when she clicks to open a folder to access the saved emails only once did a folder show the saved files!

I will be going over to my friend this afternoon and check again and try on different browsers and possibly Thunderbird

Update
Tried BT Mail again in IE11 and Chrome had the same problem, personal folders were erratic, sometimes they opened and sometimes they wouldn't!
I decided to install Mozilla Thunderbird and added the BT Mail without a hitch! All personal folders were transferred with the save emails and able to open them!

In conclusion, BT Mail seems to hang when I connect via BT.com although the internet connection is around 13Mbps but no problems using Thunderbird!