The 2 main pillars of digital marketing are online marketing and offline marketing. I’ll only mention the different areas of online marketing here, for the sake of completeness.
The 7 big categories of online marketing are:
Search engine optimization (SEO)
Search engine marketing (SEM)
Content marketing
Social Media Marketing (SMM)
Pay-per-click advertising (PPC)
Affiliate marketing
Email marketing
http://www.multaisolutions.com/ecommerce.html