In those cases, it is impossible to track whether the respondent has already answered this survey or not, as we track the participation history using the respondent's browser local storage, which is unique for the browser or device.

There also might be other reasons why you are getting duplicated answers:

If you are getting duplicated responses to your email survey, please check your survey settings in the Configure tab. You might need to disable these two options to avoid duplicated responses from your customers:

Once disabled, the respondent will not be able to answer the survey multiple times, unless he is using another browser, device, incognito mode or clear the cache.

If you embed the first question of your survey in the email, in the rare cases you might get multiple irrelevant duplicated responses from the same customer registered at the same time - see an example below:

Those duplicates are caused by security add-ons or link scanning software installed on the respondent's device. The way it works is that the software scans the link and opens it before the user does, and that's how those fake responses (bot clicks) are registered. You might notice the duplicates registered with the real customer email or with an irrelevant email, as in the screenshot above.

To prevent this, you might need to use Email answer confirmation feature, which is enabled by default for all the new email surveys.

You can find it in the Create tab ➡️ Settings ➡️ Survey Experience. Once it's enabled, we will ask the respondents to confirm their response to the first question on a survey landing page, so we can register only valid responses.
​

That will prevent duplicate issues in the future, but when it comes to the ones that were already provided, the only way is to delete them manually.