I took my own advice and wrote to the top and received the following reply:
I can confirm that we are continuing to transfer our customers over from BT Yahoo Mail to the BT Mail platform.
This isn’t something that can be done overnight and will be done in batches to ensure all is done correctly.
I then checked my email account and both addresses are now on BT Mail.
Just in case anybody thinks this statement is accurate and that by asking BT you will be migrated from BTYahoo to BTMail. The statement is not correct. The email migration is still on indefinite hold with no plans to re-start it anytime soon.
It is also the case that individual email accounts will not be migrated while the migration is on hold.
The email checker that was used for the above and the link posted in message 18 is not working correctly and can give false information. This was notified to BT a few moths ago but as yet it would appear that it is still not fixed.
The only accurate method to check is as per the link in message 19.
Really really don't want to go down that rabbit hole again......
What has happened to your account has also happened to mine. Without being informed we have been transferred to a BT Mail interface in MyBT but we still have BT Yahoo email accounts. I have been trying to get this documented by BT and have been having some success. However I am delaying pursuing it further until January 2017.
You will have noticed that the link to the Email checker has been removed from the Announcements at the start of the Email section of the Community.
However this discussion is off topic and if you wish to continue it I suggest we use your thread above.