The other day, one of my online subscribers, CR, complained about the e-mail marketing of a famous Internet marketer.

 “I unsubscribed from his list,” she told me haughtily. “As soon as I joined, I got e-mails from him once or twice every day – and there’s no one I or anyone else needs to hear from that much.”

 That begs the question: how frequently can you e-mail your online subscribers?

 Or: how much e-mail is too much?

 People have lots of opinions about this issue, which they support with arguments that are both passionate and logical.

 The problem is: their opinions are wholly subjective.

 The fact is: there’s an easy way to objectively and accurately determine the optimal e-mail frequency for your online subscribers.

 How does it work?

 Well, every time you send another e-mail blast to your list, a small portion of your subscribers will opt out of your list.

 Why?

 They decide that your content is no longer of value to them … or you are doing too much selling … or they don’t like your style … or you are e-mailing them too often.

 The “opt-out rate” is a Web metric that you can measure: the percentage of online subscribers who unsubscribe from your list per e-mail blast.

 A 0.1% opt-out rate means that if you have 10,000 online subscribers, 10 unsubscribed after getting your most recent e-mail.

 When your opt-out rate is around 0.1% or less, you can rest assured that you are not sending too many e-mails to your list too often.

 If you were, the opt-out rate would be higher.

 On the other hand, when your opt-out rate gets much above 0.2 to 0.4%, you are losing subscribers at too rapid a rate.

 For instance, if you have 10,000 subscribers and an opt-out rate of 1%, you lose 100 subscribers every time you send an e-mail to your list.

 You should measure and keep track of your opt-out rates with every e-mail you send.

 Adjust your e-mail frequency, ratio of sales pitches to content, message length, and topics until your opt-out rate hovers around 0.1% to 0.2% or less.

 Now, watch what happens if you increase the e-mail frequency – for instance, go from one e-mail per week to two e-mails per week.

 If you get a sharp upward spike in the opt-out rate – double or more – your subscribers are telling you they don’t want to hear from you that often.

 And you should probably eliminate the extra e-mail.

 On the other hand, if you add an extra e-mail per week and the opt-out rate does not rise significantly, you are safe in continuing at the higher frequency.

 But should you?

 Yes.

 We have lots of preconceived notions about what our market wants — and doesn’t want.

 And one of these preconceived notions is that people don’t want too much e-mail.

 But when the opt-out rate is low, your subscribers are telling you they DO want to hear from you often via e-mail.

 That’s important, because the more times you can reach out to your list with a valuable offer or content, the more money you make online.

 My colleague Amy Africa, a top consultant in B2B e-marketing, says that one of the most common online marketing mistakes is not e-mailing your list frequently enough.

 And by making that mistake, you are leaving money on the table.