BrightWave's Simms Jenkins writes in with rules of thumb for how often you can email your customers.

One of the most frequent questions I’m asked is “how often should we send email messages to our list?” Quite simply, there is no simple and catch-all answer to that seemingly easily yet complicated (and loaded) question. In this column, I will outline several rules of thumb that should help you make educated decisions regarding the optimal frequency mix for your email marketing deployment calendar.

Not too much and not too little

"Well, Simms, thanks on that one," you may think. While establishing maximum frequency guidelines is a must (such as never more than two emails per month, per user), companies should also consider minimum standards as well. Whether your list is 500 or 500,000, you should mail to it on a quarterly basis at the very least. If you do not meet this minimum threshold, you risk diluting the power of permission that you achieved when you acquired them as an opt-in email subscriber.

Think about it: You may have signed up for various newsletters, updates and alerts from trusted websites and brands, but if you don’t hear from them for five months, you may grow disinterested or -- worse -- forget that you granted them permission to send you email communications in the first place. Infrequent messaging could lead to a rise in unsubscribes. I call this the relevancy of frequency factor.

Never more than once within 72 hours

All bets are off on this one if the email is triggered based on breaking news (e.g., CNN Breaking News Updates) or other timely content, but with regard to a general newsletter or promotional piece, you should abide by this rule or run the risk of generating unsubscribes and low response rates.

If you didn’t achieve the results you wanted on Tuesday, altering the message and redeploying it on Friday may get the VP of Marketing off your back but it won’t change the way recipients view your email.

One regional retailer that I opted in to has sent me two emails within the past two days (one was for a women’s special but that is a different story). I promptly unsubscribed and hope to never see an email from them again. The relationship (off and online) they built with me was hurt by their too-frequent email deployments. This is every email marketing manager’s worst scenario.

Frequency segmentation

Many companies wisely use list segmentation to determine the types of content and offers in order to send different customers, but you should also use this technique to determine optimal frequency rates. While one group of customers’ responses may be higher with mailings every week, another group may respond better with a monthly frequency. Marketers should adjust frequencies for different types of customers based on list segmentation.

Better yet, quit playing the guessing game and ask customers directly what frequency they would prefer at the time of opt in. This will save you dollars on costly market research and segmentation and ensure that your customers get exactly what they what.

Use your metrics

Frequency should not be as simple as "we don’t mail to our customers more than twice a month." Just like any marketing and sales program, email marketing campaigns should be adapted based on the responses to each program. Email provides marketers with more info than almost any other marketing medium, and this data should be used to evaluate and establish your frequency mix.

For instance, if 14 percent of users clicked on the “Buy” link in your email but only 10 percent of them completed the transaction, wouldn’t you consider the ones who clicked but did not buy your hot leads?

In the offline world, you would probably focus your sales resources on converting this 10 percent. With email, you have it easier. Tailor a campaign to these folks who have expressed an interest in your product or service, test the creative and offer, and then send it about a week after their original click-through. Keep a close eye on their response.

Should you resend an email that soon to the rest of your list? No. The point is to use your metrics as a map to adapt the battle plan and convert the low-hanging fruit.

Rules should guide, not restrict

The key to establishing the right email frequency with your customers, as in every aspect of email marketing, is to plan, test, adapt, analyze and refine. Each marketer will find that different rules apply for their customers. Though the guidelines I've outlined should help you establish rules for your organization, the key is to always be flexible as customers’ desires and preferences are quick to shift in this space.

If you have any real life examples of what worked and what didn’t in establishing the right frequency, please let me know. I will share the results in a future column.

G. Simms Jenkins is Founder and Principal of BrightWave Marketing, an Atlanta based Email Marketing and Customer Relationship Services firm. He has extensive relationship marketing experience on both the client and agency side. Jenkins has led BrightWave Marketing in establishing a large client list, including marquee clients like GMAC Insurance, CoreNet Global and The Atlanta Journal - Constitution. BrightWave Marketing has become a leader in the Email Marketing outsourcing space by using their expertise in strategy, design, list management, segmenting, delivery and analysis. Jenkins has been recognized by many media outlets as an Email Marketing and CAN-SPAM expert. Prior to BrightWave Marketing, Jenkins was Director of Business Development at two high-tech start-ups and headed the CRM group at Cox Interactive Media, a unit of media giant Cox Enterprises.