Most interior designers keep their portfolio on their website.  There may be a little information about their services, but mainly interior design websites are put up to display designer's work and contact information.  Some interior designers even have a blog. Although, I'd suspect that if those designers are reading this article, their blog probably hasn't been updated in awhile.

While interior design websites have a way for clients to contact the designer, they usually haven't created a way for the interior designer to contact clients.  This is where an email list is useful to your business.  Despite the spread of social media, email is still one of the best ways to be in contact with your potential clients and past clients - the ones that you don't talk to regularly.