Duplicate Subscribers in Mailing Lists

We're currently developing forms that submit a users basic details and mailing list preferences (3 options).

Upon submitting the form, the preferences are used to input the user's data into the relevant Sitefinity Mailing Lists. i.e. If I select all 3 options, my details are added to 3 mailing lists.

Currently, the form created does not recognise whether or not the details being submitted have already been added to the mailing list(s), meaning I can submit the same details as many times as I want.

I have 2 questions:

1. Does Sitefinity's e-mail campaign tool recognise duplicate email addresses, and thus prevent more than 1 email being sent to the same email address? 

2. Is it possible to expand on the form function, so that upon submission values are validated and those already contained within a mailing list are recognised, and the user is notified that their details are already contained within the selected mailing list.

Thanks

Josh 

Hello,

The mailing lists identify the subscriber by the email, as a result, you cannot add a subscriber with an email that is already in the mailing list when working via the UI. When sending emails to a list, Sitefinity will send emails to all subscribers in the list. That is why, a check should be performed when adding the subscriber to list to ensure that there is no existing email in the list. The sample in the documentation checks this before adding the subscriber to the list:Add subscribers to mailing lists.

The best approach would be to enhance your form to perform this check before adding the subscriber to avoid duplicates.

Regards,
Atanas Valchev
Telerik