security – setting up alias account details

My issues are a) when we are sent a code by email, what is the format? I (and others) are just not getting the codes and methinks it's because we have set up filters with our ISP to stop 'junk' hitting our inboxes. E.g. one of my filters blocks some comms where the word 'security' is a keyword. Point b), because of the issue with a), I want to provide a mobile/cellphone number so you can send a code there but the way to do it is not evident without the possible risk of wiping my alternative email addresses (one of which has the issues mentioned in my point a). Can anybody help please? As a rider, my problems all seemed to stem from changing my password . . . perhaps we should not be so brainwashed into doing this??