Autodiscover doesn't work with username and email address having different formats

I have Autodiscover, it works fine within the domain.

However, outside the domain, after entering the email address and the password, it will produce a prompt asking for username and password.

Our domain usernames are consisted of the first letter of the first name and then the full last name.

John Smith username will be JSMITH and the email address will be john.smith@company.com

I found that if I change the username to john.smith instead of jsmith the autodiscover will work without asking for username and password.

Is there a way to have autodiscover work with keeping my current usernames of jsmith without having to rename all the domain usernames to be in the same format as the email of john.smith@company.com ?

Thanks.

http://peteroy.blogspot.com/