My btinternet email was locked due to unauthorised use. I have contacted BT and cleared everything and changed my password to two step authentication. I have also changed the password in the Windows 10 settings. However the red triangle still shows and I am not receiving any emails. I have downloaded Thunderbird as a temporary measure and that setup with no problems. Also there was no problem resetting my phone, so why the problem with eMClient?
What is the error as defined in MENU > ERROR tab?
Have you tried temporarily disabling anti-virus and VPN software?