Double opt-in. What is it and how does it work?

Double opt-in is a way of subscribing in which a person, after filling in a form, also clicks a link in a verification email. By doing so they confirm that the address is theirs and that they really want your emails. You gain fewer contacts than without verification, but they are real people who open emails, and you can prove the consent. Below you will find how double opt-in works, what the data say about it, where it stands with GDPR and how to set it up in Quanda.

In a nutshell

1. Roughly two senders in five use double opt-in (Sinch Mailgun, 2025).
2. Thanks to it, typos, made-up addresses and other people's addresses do not get into your database.
3. GDPR does not explicitly prescribe it, but you must be able to demonstrate consent. Double opt-in is the simplest proof.
4. In GetResponse data, lists with double opt-in have an open rate of 35.72 % against 27.36 % for single opt-in.
5. The price is slower growth of the database: a sign-up rate of 0.33 % against 1.28 % for single opt-in (GetResponse, 2022). Some people do not click the verification link.
6. In Quanda you turn it on in the active form on the Double opt-in tab. There can only be one link in the verification email.

In short: what it is, when to use it, what it brings and what it costs

• What it is: a two-step subscription. A form and then confirmation by a click on a link in an email.
• When to use it: whenever you gain a new contact through a form on the basis of consent to the processing of personal data.
• What it brings: verified addresses, provable consent, better deliverability and a higher open rate.
• What it costs: an extra step for the subscriber and fewer new contacts than with a subscription without verification.

What has changed since the article was published: The original Czech article came out in April 2018, a month before GDPR started to apply. We have added a comparison with single opt-in, data from practice, an overview of how authorities and courts in neighbouring countries view double opt-in, and the steps for setting it up in Quanda. In addition, Gmail and Yahoo since 2024 and Outlook.com since 2025 have been judging spam complaints and undelivered emails more strictly, so a clean database carries more weight than before.

What is double opt-in

Double opt-in is the verification of the owner of the email address who is filling in a form. "Double" as in "twice" or "twofold". "Opt" is short for "option", meaning a "choice" or a "wish". "In" is the preposition, as in "into" or "inside". We could therefore describe "opt-in" as a wish to be added to the database of your contacts.

Double opt-in is thus a double confirmation of that wish. The first time by submitting the form, the second time by clicking the link in the email. You will also come across the term confirmed opt-in.

Single opt-in is a subscription without verification. The contact appears in Contacts as soon as the form is submitted, and nobody checks whether the address entered exists and who it belongs to.

How double opt-in works

Once this feature is on, the data filled in the form is saved and a verification email (also called a confirmation email) is sent to the email address given in the form. This verification email contains a request to verify the email using a specific link, which the subscriber has to click for the verification to succeed.

In Quanda you can edit the content of the verification email, including the verification link, exactly as you need. After verification through double opt-in, this information also appears in the contact detail and when the contact is exported.

Until verification, you see the data filled in only in the record of the completed form in the Completed forms section, not in Contacts. The record there is marked as awaiting verification. If the person does not click the verification link within 7 days, Quanda deletes their email and all other personal data from the form, both from the application database and from the record of the completed form. The record stays in the list of completed forms, but without any personal data.

Single opt-in and double opt-in: a comparison

What the data say: double opt-in in numbers

The most extensive public comparison was published by GetResponse. It compared its customers' lists with and without verification across 2.76 billion newsletters sent in 2022.

People who confirmed their subscription therefore open emails roughly a third more often and click roughly three quarters more often. The same data, however, also show the other side of the coin.

Source: GetResponse, comparison of single opt-in and double opt-in, 2.76 billion newsletters, data for 2022.

There are two things worth taking away from the table. Double opt-in is not a magic trick that solves undelivered emails by itself. An address verified today may cease to exist in a year, which is why you have to look after your database continuously. And the difference in the sign-up rate is large. That is why it pays to put care into the verification email, so that as many people as possible confirm it.

An older Mailchimp comparison from 2011 on a sample of 30,000 users came out even more favourably for double opt-in. It reports 72.2 % more unique opens, 114 % more clicks and 48.3 % fewer undelivered emails. It dates, however, from the time before large-scale database cleaning and privacy protection in mail apps, so treat it only as a supplement.

How many senders use double opt-in

Double opt-in is therefore used by roughly two senders in five. If you turn it on, you will have a cleaner database than most of the others.

Why use double opt-in

You verify the owner of the address. You can attribute the consent to a specific person, not just to a row in a table.

You get rid of typos. Someone who does not receive the verification email usually notices the mistake and subscribes again with the correct address.

You keep made-up addresses and other people's addresses out of the database. Without verification, anyone can enter an address into the form that does not exist or belongs to someone else. In the first case the email is not delivered, in the second it reaches a person who has never heard of you and marks it as spam.

You protect yourself against bots. Automated scripts can flood an unprotected form with thousands of other people's addresses. Spamhaus, the organisation that runs lists of blocked senders, therefore recommends confirmed opt-in as a basic measure. According to Spamhaus, it prevents unwanted subscriptions caused by forgeries and typos and gives the sender a provable trail when a recipient reports an email as spam.

You help deliverability. Mailbox providers rate senders by undelivered emails and complaints. In its policy for senders of bulk messages, Seznam.cz recommends verifying the contacts you gain precisely by the double opt-in method. What happens to addresses an email is not delivered to is described in the article Reasons for undelivered emails.

When to use double opt-in

Whenever you gain a new contact on the basis of the legal basis for processing personal data called "Consent". This feature makes sure you verify the owner of the email. Since everything shows up with the contact in Contacts once the subscription is confirmed, you can very easily prove at any time that consent was given.

Tip: With a lead magnet, remind people in the verification email what they will get after confirming. That gives them a reason to click the link straight away. How to build lead magnets is described in the article Lead magnets in B2B marketing: what brings in quality leads.

Double opt-in and GDPR

In connection with GDPR this is a very useful tool that helps you prove unambiguously who gave you the consent. Without this feature you will find it hard to demonstrate that the consent was given by the very person who owns the email address.

GDPR does not explicitly prescribe double opt-in. Article 7, however, says that the controller must be able to demonstrate that the data subject has given consent. How you demonstrate it is up to you. Individual countries differ in how strict they are.

Source: GDPR, Articles 7 and 32; Act No. 480/2004 Coll.; judgment of the German Federal Court of Justice of 10 February 2011; decision of the Austrian data protection authority of 9 October 2019.

Warning: Double opt-in does not replace the consent itself. The form must still contain an unticked consent box and a link to its full wording. The verification email only confirms that the consent was given by the owner of the address. This article is not legal advice. If you send to Germany or Austria, consult a lawyer.

What the consent must contain and how to record verification and legal bases for contacts you import into Quanda is explained in the article GDPR in email marketing: consent, legal basis and contact import.

How to set up double opt-in in Quanda

In Quanda, double opt-in is part of every active form. The feature is available in all plans at no extra charge and setting it up takes about 10 minutes. An active form is a form created in Quanda that you place on your website and that saves contacts straight into the database.

1. Open the active form you use to collect contacts and switch to the Double opt-in tab.
2. Turn on the email address verification with the slider in the first section.
3. Fill in the subject of the verification email so that it is clear who is writing and what the recipient should do.
4. Write a short text of the verification email without images, stating what the person is subscribing to.
5. Insert the verification link, which was generated automatically. Either leave it at the cursor position as a web address. Or write the link text, select it and click the Insert verification link button.
6. Check that there is only one link in the email, the verification one. Delete the original sample link.
7. Fill in the form yourself, confirm the subscription in the email and keep an eye on the Completed forms section to see how many people did not complete the verification.

Warning: There can only be one link in the verification email for the verification to go through correctly. Do not add a link to your website, social networks or a signature with a web address.

The procedure with screenshots is in the guides Double opt-in and How to create and set up an active form.

How to write a verification email that people confirm

The verification email has a single job. To get the person to click the link. We recommend keeping the content as simple as possible: a text that is clear, brief, to the point and without images. A simple email has a better chance of being delivered to the main inbox folder, and the recipient confirms it within a few seconds.

An example of a verification email:

The verification email and the welcome email are two different messages. Leave the thank you, the introduction of your company and the promised file to the welcome email from the form automation.

What increases the number of confirmations

• A sentence on the thank you page of the form saying that a confirmation email will arrive in the inbox.
• A subject that makes it clear who is writing and what the recipient should do.
• A sender with a name the person knows from the website.
• A short text without images and with a single link.
• A verified sending domain, so that the email does not end up in spam.
• A regular check of the Completed forms section.

When there are many unconfirmed subscriptions, look for the cause. In the form, in the Completed forms section, sort the list by the subscriber column. At the top you will see rows with a dash in place of the subscriber. Those are the people who did not complete the verification. More in the guide Completed forms. Verifying the sending domain is described in the article Gmail, Yahoo and Outlook requirements for bulk email senders.

Final word: is double opt-in worth it?

A smaller database made up of people who confirmed their address is better than a large database full of addresses that do not exist. The quality carries over into the deliverability of all your future campaigns.

Do you have more questions about GDPR and Quanda? If so, write to us at support@onquanda.com or call us on +420 605 163 892. The context is explained in the online courses GDPR and Email Marketing in Practice and Collecting contacts: forms and lead magnets. If you would like to go through your form settings together, book a free consultation.

We wish you a life without GDPRoblems.