I've had a few emails from people who would like to change their email addresses in Passport but dont have the option.
I tried looking at the other two passport accounts I've got and found that I couldn't change the email addresses for them either.
It turns out that you can change the email address for accounts that are on non mail hosted sites. What this means is that you can change some, but not others - it depends on your email address domain.
For example - you cannot change your email address if your email address is on a hotmail.com or microosft.com address, but you can if you are on a "mydomain.com" address (generally).
There are other domains you cant do either - the point is that you can do some, but not others. If you dont have the option, you wont be able to change your email address.
Why is this the case? Its all to do with the way the mail for the domain is managed and unfortunately I dont know the details to be able to be more specific than that (sorry).