What is Spintax?
Syntax like {Hi|Hey|Hello} that picks one alternative per send, so no two emails from a sequence are byte-identical.
Bulk filters look for many identical messages from one sender. Spintax varies wording automatically — {Hi|Hey|Hello} {{first_name}} — so each send differs slightly, in the same way a person's emails do. Combined with personalisation variables it makes a 2,000-send step produce 2,000 distinct messages. Keep the alternatives natural; spun nonsense is worse than repetition.