Jessica Tsai has written up a comprehensive piece on email marketing over at DestinationCRM that covers deliverability, authentication, ROI, and getting people to open and click.

Some highlights from the article, plus links to related email marketing resources from MailChimp, are below.

What’s the ROI for email marketing?

According to the Direct Marketing Association, email marketing is projected to return $43.52 for every dollar spent in 2009.
See also:

Tracking ROI from your email marketing with MailChimp

Case Study: $157,000 from one email campaign

Google Analytics Blog: Tips for tracking email marketing campaigns

How much email gets lost?

“A very small percentage of emails the ISPs [Internet service providers] handle is legitimate—90 percent of it is spam,” says David Atlas, senior vice president of worldwide marketing and sales for certified email provider Goodmail. Of the ones that are legitimate, email deliverability vendor Pivotal Veracity reports that roughly 20 percent don’t even get delivered.

See also:

Deliverability on the MailChimp blog

Check your email campaigns in major spam filters with one click

MailChimp’s List Activity scores launching soon

What’s the definition of spam?

“Consumers today see less spam than they’ve seen in the past,” MAAWG’s Stiles says, “[but] there’s actually more spam than there’s ever been.” But even if you’re not selling Viagra, spam is in the eye of the beholder. Some experts define it as anything a recipient doesn’t want; if the request was for emails to be sent monthly and you send them daily—you’re spam. “Companies will say, ‘But I’m CAN-SPAM compliant,’” Stiles notes. “[That] means you won’t wear an orange jumpsuit and handcuffs. It doesn’t mean you have the right to send email.”
See also: How legit email marketers can prevent spam complaints

Is authentication important?

David Daniels, a Forrester vice president and principal analyst, anticipates that by the second quarter of 2009, if a sender’s address is not authenticated, it won’t just be more-carefully screened—it will be immediately dropped.
See also:

Authentication is related to deliverability

MailChimp email authentication guide (see which ISPs check for which forms of authentication)

Will Yahoo block messages that aren’t authenticated?