Dynamic content
Parts of an email that change per recipient — blocks shown, hidden or filled differently.
Dynamic content goes further than a merge tag: instead of swapping a word, it decides whether a whole block appears. One campaign can show different products, prices or language depending on who opens it.
The rules live in the sending platform and are evaluated as the message is built, so what each person receives is a fixed email — it does not keep changing after delivery. Content that updates after the fact is AMP for email, which is a different mechanism.
The practical cost is testing: every branch is a version that can break, and preview tools only show the ones you remember to check.