I am currently on Virgin Network, but use BT Email system. My laptop has the Norton Security Suite including Secure VPN.
It is taking 2 or three attempts before I get to emails, and sometimes when sending BT blocks outgoing messages with the excuse that I am phishing.
I switch off Secure VPN and everything works ok. Is it Norton or is it BT mail?
I have been in touch with Norton, and they say it might be BT.