Accounts, also called Profiles, on the conference website are always associated with a single email address. Of course many people have multiple email addresses and may end up with multiple accounts. While it is fine to have multiple accounts if one desires often it is preferable to have a single account that can be used but still have access to parts of the system which may be associated with another email address. This is particularly true for paper authors where the email on a paper might not match the email address used to log into the conference.
If you wish to link multiple accounts (email addresses) you can do so by "merging accounts". You can merge an account for a conference at the following urls: