Because there is so much emphasis placed on online marketing, offline emarketing presents a very good opportunity. It's not old hat as some will claim and it's proven to work.
A combination of online and offline marketing tends to get the best results although this is a generalisation because it depends on the product and market.
One of the issues with email marketing is that people think it's free. Well, that's true, but with a caveat. It's only free if it gets to the reader. With spam filters becoming increasingly difficult to by-pass, if your message ends up in the black hole when your prospect would have bought, then it's cost you a sale - and a potential long term customer. That, is expensive and you'll never know what it's cost you.
You could say the same for direct mail too.
As we all say, you really need to test in order to identify the optimum marketing mix for you.