Email subscription management is not in the product scope of Simple Survey and is best incorporated into your organization's broader communication management approach.
Organizations typically track many different communication types, allowing their audience to select which types of communications they want to receive. Also, with privacy considerations and laws such as the General Data Protection Regulation, email subscription management should be accessible to your audience from one location for the best possible experience.
Once you have established a data point for whether a person would like to receive surveys or not, you can incorporate this logic into the workflow or other automation used to send surveys.
For example, you could create a checkbox field on Contact called Survey Opt-Out, and include a checkbox question in your survey that asks the recipient if they want to be excluded from future surveys. Once the survey is received, use Process Builder or other local automation to update that field on Contact if a response is received with the survey opt-out question checked. In your survey sending automation, you would check for this field on Contact. This method works very similarly to our Survey Fatigue feature included with Simple Survey.
If you are looking for a simple all or nothing solution, there is a free app (which hasn't been updated since 2009 but recent reviews show that it still works) from Salesforce Labs which may help: https://appexchange.salesforce.com/listingDetail?listingId=a0N300000016YDZEA2
Please note that Internet Creations cannot provide any support for Salesforce Labs applications.