Double Opt-in Turns 15: Looking Back, Looking Ahead

Eric Thomas, L-Soft Founder and CEO

In 1993, LISTSERV® was the first email list management software to introduce double opt-in subscriptions for people joining a mailing list. With the 15th anniversary of double opt-in upon us, Eric Thomas, L-Soft founder and CEO and LISTSERV creator, answers some questions about this best practice and gives us a glimpse of what's to come in the next version of LISTSERV.

Q: What led to the development of the double opt-in feature in LISTSERV?

A: The double opt-in feature, named address verification at the time, was primarily a mechanism to deal with subscribers from unreliable networks or ISPs. Back then, many burgeoning ISPs lacked the resources to help their customers set up their email clients, and it was not uncommon to get mail from addresses that you could not reply to. A side effect of the new feature was that you could no longer "spoof" subscription requests and add people to busy discussion lists against their will.

The double opt-in feature was released with LISTSERV version 1.7f in March 1993. You can read the original announcement of the new feature here:;jdDFXg;19930315031254%2B0100

Of course, that was long before the concept of permission-based email marketing – in fact, it was long before email marketing itself. People often tell me that I should have taken a patent on single opt-in in 1986 and another one on double opt-in in 1993, and I would be one of the richest guys in the world. Well, maybe – I guess I will never know. But one thing is for sure, if I were charging royalties for the use of double opt-in, there would be a lot more spam in our mailboxes.

Q: How do you see the future of double opt-in email?

The technology itself is stable, although there is always room for improvement. But there is a missing link. I think double opt-in would be a lot more useful and widespread if there would be a standard way for the mailing list to communicate with the subscriber's email client and request a subscription confirmation that, if approved, automatically whitelisted the mailing list in the client, guaranteeing delivery of future messages from the list. The subscriber could revoke this at any time, and the client would then automatically tell the mailing list to remove the subscriber. I am sure spammers would try to abuse this process, but it would still be a big step up from what we have today. And the confirmation could optionally be coupled to SSL certificates so that subscribers would see the real identity of the company operating the mailing list and see a green/red/white address bar. This would bring email fraud-protection technology in line with what is available for secure web sites today.

Q: Is there anything people should pay attention to when implementing double opt-in, any advice you would give?

A: As always, test the double opt-in feature thoroughly. Every email list should have a customized confirmation message that should, ideally, double up as a welcome message. And this welcome message should clearly indicate the nature and expected frequency of future messages from the list. As some subscribers resent the "hassle" of double opt-in, it can be a good idea to explain that this simple one-click step is for their protection.

Q: Can you tell us a little bit about what's coming up with LISTSERV?

A: Sure, we are finishing up a new version that includes an HTML editor, a new email list home page organization and new features in the message posting interface. In particular, you can scan your newsletter against a popular spam filter as you are typing it in the HTML editor. Sometimes, small changes to the format or wording of the newsletter can make a big difference in deliverability. We have also improved the LDAP interface and introduced changes to reduce back-scatter.

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