Double Opt-in for Better Delivery Rate?
Building a list is one of the fundamental elements of doing business online. I have often been asked by clients whether their email list should be double opt-in or single opt-in.
Despite the ramblings of various "gurus" on the subject, my feeling is that both double opt-in and single opt-in have advantages and disadvantages that makes the choice more complicated than just saying all email lists should be one of the other.
The key question here is whether or not you have the recipients permission to send them email. And that question is at the root of almost all of the arguments for double or single opt-in. We're going to discuss this issue in a future post, so for now we'll assume that you have the recipients permission.
Most emailing list software that you install on your own server allows you the option to choose single or double opt-in. You can usually set the option differently for each email list you are building. So, some of your lists can be single opt-in and some can be double. We use both AutoResponse Plus (ARP) and SubscribeMe Pro (SMP). Both of these allow choice of single or double opt-in in specific mailing lists, but only ARP has a built-in autoresponder, a distinct advantage.
Many online services used for building and emailing lists, but not all, require the use of double opt-in. We have used ConstantContact in the past, but now use aWeber and AutoContactor exclusively because they include autoresponders. aWeber only allows double opt-in, but AutoContactor allows both single and double opt-in options.
Single Opt-in vs. Double Opt-in
In a single opt-in system, the subscriber fills out a form to join your mailing list, clicks the submit button and they are instantly added to your list. In double opt-in, the subscriber fills out the form, clicks the submit button and they are immediately sent a confirmation email. If they click on the link in the conformation email, they are added to your list. If they don't, they are not.
You can easily see the dilemma here. If you are using double opt-in, a lot can go wrong between your subscriber clicking the submit button and their actual addition to your list.
The confirmation email can get lost, it can be trapped by the recipients spam filter, they can have "buyers remorse," or they can just get distracted and not click the confirmation link.
We have found that our verification rate on double opt-in is about 50% on most of our lists. That means that only half of the persons who click the submit button on the sign up form ever complete the process and get added to the list.
On imported lists, we have tested and found that somewhere from 20%-33% of imported email addresses ever verify. And some of that can be traced to some of the weaknesses of single opt-in mailing lists.
OK, let's use some of your actual numbers to weigh out the advantages/disadvantages of single vs double opt-in. As we stated above, our numbers show that we lose half of prospective subscribers by requiring double opt-in. You'll have to plug-in your own numbers here to evaluate your own circumstances.
So we start out with half the subscribers. But our "open rate" on our double opt-in lists averages out at 56%. On our single opt-in lists, the average "open rate" is 31%. OK, we've got half the subscribers but almost double the number of actual readers.
How many emails actually got delivered?
Undeliverables are the bane of emailers. Bad addresses (intentional or out-dated), full mailboxes, typos on the subscribe form all add to the undeliverable rate. Some ISPs may block mail from IP addresses whose undeliverable rate to their users exceeds 10% repeatedly. Our double opt-in lists are averaging 1.2%-2.1% undeliverable.
But not surprisingly, our single opt-in lists have an undeliverable rate of 2.7%-5.9%. That is lower than the 10% threshold, but over twice as high as the undeliverable rate on the double opt-in lists.
Response Rate (Click Through Rate – CTR)
I don't put too much stock in the "open rate" figures for my emails for the reasons outlined below. As far as I am concerned the percentage of people responded to the "call to action" in the email is far more important. We've tested CTRs on both single and double opt-in lists and found CTRs of 29% in double opt-in mailings vs. 12% in single.
Why all the differences that seem to favor double opt-in?
Subscribers that make the effort to sign up, then confirm are usually more committed to your list than those who can fill-in, submit and run. They are more likely to give you a real email address (because what's the point in giving a bad address if it has to be confirmed?), more likely to open your emails once they've received them and more likely to click through on your offer.
So why would you EVER want to use single opt-in? Well, there are a few good reasons, but I think those will have to wait for a later post.
"Open Rate"
Open Rate is a measure of how many of your email recipients actually "opened" your email. That doesn't necessarily mean they read it anymore than opening an envelope means you will read the letter inside – but it is at least an indication that enough interest was generated to get them to click on it.
The "open rate" is determined by the use of a single-pixel gif (usually) in the email. Each time the email is loaded, the gif loads too. And that can be counted on the host server. Divide the number of times the gif has been loaded by the number of emails sent and you have the "open rate."
There are some issues with this number. It only works in the HMTL version of your email, so those seeing the text version will not be counted. These days, most subscribers have the HTML setting turned on, so this may be less of an issue than in the past.
The other problem is that the gif loads EVERY time the email is loaded. SO if a subscriber clicks on the emil several times, it will be recorded as an "open" each time. I have had mailings with an "open rate" of over 400%. Either I dazzled them or confused the hell out of them – only the click through rate (CTR) will settle THAT issue.
If you get the feeling that you've read this before, it's not blog deja vu; I posted nearly the same post at the 
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