I use the BT email app on my laptop. It generally works fine apart from being very slow to delete emails after selecting them. I thought it was linked to the speed of my wifi but we've just updated to fibre and it's precisely the same. Gmail works fine so I suspect it's an issue with the BT app. This extends my time administering emails considerably so I'd like to resolve this if possible.
Ditch the BTMail client/ app and use one of the many superior free ones such as Thunderbird.