The simplest way to do it is to temporarily create the 2 accounts as IMAP in Thunderbird and simply drag and drop the items between accounts.
The easiest way will probably be to use an email client such as Thunderbird or Outlook set up as an IMAP account.
Add your BT account and this will synchronise all your folder and emails from the BT servers with the email client. You should then add your Yahoo account to the email client then drag or copy the "BT" folders into the Yahoo account on the email client. This will then synchronise them with the Yahoo account on the Yahoo servers.
You can then delete the accounts, not just the folders, from the email client if you want. Personally I would just use an email client in the first place and there would be no need to use your BT or Yahoo accounts using webmail.
This really is a huge problem and completely untenable in this day and age of high tech as we too use our own domain constantly. No one knows us by our real BT email address and won't recognise any email sent from it.
BT has made this feature available for all the years that we have used BT and we use it 100% of the time. This morning, by moving us to the "new" BT mail you have completely degraded your email service by taking the alias feature away from us. What's the point of us being with BT if I now have to not use BT webmail and find another way?
How can this be "new" when it's a reduction not improvement in features?? Will have to seriously consider us continuing to use BT! In the meantime, how do we get moved back to the Yahoo version of BT mail? thnx
In the meantime, how do we get moved back to the Yahoo version of BT mail? thnx
Your email account was migrated away from the BTYahoo email service which was owned and operated by Yahoo onto the "new" BTMail email system which is owned and operated by BT.
You can not be moved back to the Yahoo email system.
I guessed that to be the case but if you don't ask..... I've now raised a complaint with BT about this.
Not entirely sure why you think a company should be obliged to let you use their mail servers for somebody else's mail but hey ho.