They say I want an email message. They want to offer current customers some new product...or maybe an old one at a better price.

Would you call this a sales letter? Is there any difference?

The differences are only minor.

The same good old fashioned direct response principles still apply.

There are some copy considerations specific to email marketing, such as crafting your copy in a manner that doesn't displease the Spam filter gods and whatnot. But overall, copy is copy.

Some "experts" claim that because email is a more personal form of communication, the copy in your emails should be more personal/friendlier and should speak directly to the prospect. And they are right. My only problem with this advice is that ALL of your copy (email or web) should follow those rules.

So if you are doing your job right on the landing page, your email and web copy should follow the same rules.

That being said...

Because the less copy you include in your email, the more likely it is to make it through the gauntlet of filters, I have found better results lately from short emails that direct the reader to a landing page with the "full copy" message.

This works particularly well if you use the Zeigarnik effect (incomplete story or thought) in your email to maximize CTR from the email to the landing page.

I think Michel has a great case study about this exact technique in the Copydoctor Members section.

Eric