To maximise the response rate, and quality of feedback, from your relationship survey, you will want to consider your customer communications plan. Typically, this will involve a short sequence of emails, e.g. heads-up, launch, reminder(s), thank you, findings, and your improvement plans.
In addition to these emails, you may want to use other channels that are available to you, e.g. asking managers to encourage their staff to complete the survey, advertising it on your intranet, or publishing it as a news item in your regular newsletter.
Below is an example of an email-based customer comms plan.