Email marketing may not be getting all the credit it deserves. ROI numbers do not reflect the many aspects of email marketing that cannot be measured and thus, are going unaccounted for.

Take, for instance, a situation where a retailer sends out a weekly mass email to its subscribers announcing a 3-day, 60 percent off sale in the store – no coupons, just a sale announcement. The customer reads the email and, in turn, makes it a point to stop by the store before the end of the sale. This is great because it means that your email worked! Customers got the message through your email. But how do you know this for sure? Because you also have big “SALE” signs in the windows. Maybe the signs are what brought the customers in. The problem here is that there really is no way of tracking the number of customers that came in because of the email and the customers that came in because of the signs. The email could very well have brought in the majority of customers, but with no promotional code or other proof, the email ROI and response rate can appear much lower than it actually is.

A study by Epsilon discovered that a whopping 67 percent of email subscribers say that they have purchased products offline as a result of receiving an email from the retailer. This is a significant number that shows the effectiveness of email marketing that simply isn’t being measured.

Another opportunity to skew the ROI of email marketing comes when recipients visit the retailer’s website directly by entering the URL rather than clicking on the links provided in the email. Because a common measurement for email marketing is to track the number of recipients who click the links within the email, those who directly visit the site are being left out in the email reporting. The same study by Epsilon found that 33 percent of email subscribers say they generally go to websites directly, as opposed to following an email link.

Before letting email marketing fall out in the budget cuts, take into consideration some of the overlooked benefits and what they mean to your business.

E-mail marketing worldwide has increased 39.5% in Q1 of 2009, meaning that companies have been amping up their e-marketing more than ever to communicate their bottom line during these challenging economic times. And while companies are happily blasting to their heart’s content, consumers may suffer from information overload as their inboxes fill to the brim with offers, newsletters and whitepapers.

This leads to the following major understatement of the digital era:

Getting people to willingly hand over their e-mail addresses can serve as a difficult task.

So what can you do to ease the wariness of info-overloaded consumers and get them to opt into your list? We’ve put together the “Ten Commandments for Collecting Opt-Ins” to help you acquire your ultimate target audience.

Commandment 1: Ask, and You Shall Receive.

If you provide more opt-in opportunities to your consumers, chances are that your response rate will significantly increase. Structure your resources to ask for an e-mail address at every point of customer contact, such as your website home page, a guest book, customer service / support calls, feedback forms, customer surveys, brochures, invoices, tradeshows, events, etc. The more, the merrier.

Commandment 2: Strive for Simple.

Make the e-mail sign-up option on your website clear and visible and provide your audience some incentives as to how they can benefit by opting into your list. Do they get a complimentary whitepaper by doing so? A coupon? If you’re offering information, show them how the information will benefit them. Providing your targets with valid reasons to give you their e-mail addresses will likely increase your number of opt-ins.

You may also want to place the e-mail sign-up option on multiple pages other than solely on your home page. Or, you can keep it at the top of every page of your website so that it’s always there for consumers to fill out.

Commandment 3: Provide a User-Friendly Experience

The sign-up process should always be quick and easy for the customer, like asking for first name, last name, e-mail address and format preference (i.e., HTML or plain text only). Consumers are more likely to fill out an easy, straightforward form.

Commandment 4: Empower your Staff.

Train your employees to make it a habit of asking customers to sign up for your e-mail list. Make it routine for them to ask customers in the store, at the register, over the phone, or wherever else you have employee / customer interactions. Have employees ask for customer’s e=mails so they can receive your newsletter, any special promotions or to be notified about upcoming sales events.

Commandment 5: Attract your Target Audience.

To attract your consumers’ attention, use special offers such as coupons and discounts that will give the customer a reason for opting in. And instead of simply offering minor discounts, present something of substance to grasp the readers’ attention. Key sales and promotional words such as “Buy One, Get one Half Off” and “50% off” for your coupons will likely grab some attention, but it’s important to make these coupons and promotions exclusive to those who provide their e-mail addresses.

Commandment 6: Establish Credibility with Past Successes.

Another effective way to gain newcomers is to have archived or sample newsletters available on your website so they can get an idea of what they will be receiving if they subscribe. This will make customers feel more comfortable when agreeing to submit their e-mail addresses.

Commandment 7: Greet your Subscribers.

Once your customers subscribe, send them an immediate welcome message that includes what they will receive and how frequently, as well as providing easy steps to unsubscribe. If you are using an older e-mail list, and it’s been a while since you’ve sent a mailing out, ask subscribers to opt-in again to verify that they wish to continue receiving your newsletter. You should also include a phone number and physical mailing address in your newsletters to make it easy for customers to contact you about any questions or comments, and because federal legislation requires a physical address on commercial e-mail messages.

Commandment 8: Use Stealthy Subjects

When creating your subject line, avoid certain terms that may be flagged as spam, or that your customer can quickly delete from their mailbox. Make your subject line distinct so that it’s not looked over. It is also illegal to use deceptive or misleading subject lines, so keep that in mind.

Commandment 9: Establish Trust

Sending your newsletters on a regular basis, whether it’s every day, every week, or every month will help your customers remember you, and they will also begin to anticipate your messages if you stick to your regular schedule. You have to gain your customers’ trust if you want their e-mail addresses, and maintaining their trust will help keep them around.

Commandment 10: Maintain your Information.

There’s more to this than just gathering a massive opt-in list; you must continue to maintain your list and keep your opt-ins from opting out. If you’re sending a newsletter, provide your customers with useful information that not only pertains to them, but that they will enjoy reading and look forward to receiving.

If you’re sending promotions or online coupons, you’ll want to send them on a regular basis so that your customers feel like they’re constant recipients of good deals. Providing your consumers continued incentives will ensure that they stick around for a while.

Keep these ideas in mind when offering information to your targets, and you very well may be rewarded with a great list that you can use to communicate your company’s bottom line, generate ROI and keep your business flowing.