Every month our team exports, archives, and deletes invalid leads from the database. This month we noticed a significant spike in invalid leads (jump from 2k to 20k leads). After looking in these more, we see a lot of leads were delivered/opened emails as recently as yesterday and are now invalid.
I know Marketo automatically marks a lead as hard bounce - category 2, if it receives a message from the receiving server that the email does not exist. However, it seems fishy that a lead was engaging in the last 24 hours and is now invalid.
Are there any other factors used to determine a category 2? Has anyone else experienced fishy invalid numbers? To avoid deleting good leads, is it possible to edit the filters before Marketo marks leads category 2 and in turn invalid?