New computer: Surface Pro 3. IMAP protocol. Applied settings as previous machines. Outgoing set as smtp:talktalk.net.
Suspected port selections - outgoing was 25... didn't work. Referred to http://help2.talktalk.co.uk/email-settings-imap-pop3 and set to 587 with outgoing authentication. Still doesn't work.
Next suspect: conflicting firewalls? I use ESET NOD32 so sought out Windows settingsand disabled theirs.Still doesn't work. What next?