EDM marketing, also known as Electronic Direct Mail marketing, targets a large number of potential customers and focuses on fostering relationships to increase sales. While it does contain an element of email marketing (and the two terms are often used interchangeably), EDM marketing uses a more wide-reaching holistic approach. Besides email marketing, EDM also includes elements of:

• Pay-per-Click campaigns (with landing pages)
• Social Media Outreach and advertising
• Remarketing to previous (or previously interested) customers
• Offline/ Physical marketing tactics

I believe EDM marketing is an excellent strategy for businesses to gather relevant customers from various streams. 

On a personal note, when I was working at a marketing firm for several years, we always found that a wide-ranging marketing approach produced the best results for clients for the following reasons:

• We never knew which stream our next potential customer would come from (so it worked best to provide an easy avenue for customers to find our clients on multiple streams).
• Every stream or avenue you use compliments and builds off the other. 
• The more ways we created for people to find our clients, the more social proof (and clients) they received.