Having spoken to the Microsoft Outlook (MS) for Mac team earlier, they confirmed what BT Premium Mail's team told me and that is this: the reason Outlook is not syncing with BT Mail is because the two are not communicating properly, and this seems to only be the case since BT Yahoo mail migrated over to BT Mail.
MS advised that if enough people come forth with this issue they might be able to develop a fix for it, but at the moment there is no fix.
To be clear-the issue I am referring to is this: when I delete an email or move an email to a folder in Outlook-the action does not replicate/get mirrored in my BT web based mail nor in BT Mail on my iPhone. And I have IMAP settings (BT and MS checked my settings and they are all fine).
The communication between Outlook and BT's server is no longer in existence. This is awful news for those of us who use Outlook as out main email client.
I am pleading with you all to please contact Microsoft in the US (800) 642-7676 and ask to be put through to the Outlook team and report the issue. You can also reach them via their website's live chat feature. The advisor I spoke with said that they have an internal team who investigate these issues, so the more people report the issue the greater the chance of a resolution/fix.
Please ask whoever you speak with to laise with their internal support team. They are the technical people who will log this as an issue. 👍