… reach people who are not included in your e-mail list. If you got physical addresses, you can easily send out letters. For example, if you send invoices to customers, you can attach an extra letter with a link to your survey.
… survey people on the street, in public areas or physical shops. Flyers or cards are ideal for this. For example, restaurants or shops distribute cards with a QR code with a link to a customer satisfaction survey. Or distribute letters in a city or village for a neighborhood survey.
… reach people who don’t have access to email. For example, there are many seniors who don’t own a computer or smartphone. Send them a letter with easy URL that can be typed into a browser easily. They undoubtedly know someone with a device they can fill in the survey with.