In transactional email and in-app campaigns, you can apply the "Last survey date" audience filter, which gives you the possibility to target your customers based on when they've received the last survey in Retently.
To explain with a real-life scenario:
Let's assume that you're mainly surveying your customers in a recurring campaign in order to collect their feedback every 90 days. But you also have a transactional campaign, that sends surveys after a support ticket opened by the customer is closed. There is a chance that a customer will receive a survey in both campaigns in a short span of time, which will result in over-surveying your audience.
In order to avoid this, in your transactional campaign, access the Audience section.
Next, in the audience filters, choose the "Last survey date" property.
Afterward, you will have to select a condition from the list. For instance, you can choose "is more than" or "is less than" a specific number of days.
After applying the filters, only customers that match this audience rule will be eligible to receive further surveys in this campaign. In the example above, only customers that have received their last survey 30 days ago or more are eligible for this campaign. If a customer has received a survey less than 30 days ago, then they will not be surveyed in this campaign.