The “Non-interactive” category includes Gmail email addresses that are relatively young – we have started using them for email tests since October 2nd, 2023 – and where GlockApps does not mark the received messages as ‘seen’. This group of test email addresses helps test deliverability of cold emails to Gmail users who have “young” mailboxes and who have not interacted with your emails before.
The “Legacy” category includes Gmail email addresses that were moved from the seed list used in the old Inbox Insight v1.0. These addresses have been in use for years and the messages received by them have been marked as ‘seen’. This group of email addresses helps test email deliverability if your Gmail recipients have already interacted with your messages and showed a sort of positive engagement with your emails.