Esther 9:26 explains the naming of Purim from this letter — directly connected as the immediate narrative sequel.

Esther 9:29 records a subsequent letter from Esther and Mordecai confirming the Purim decree — a follow-up to this initial letter.

Esther 1:1 defines Ahasuerus' empire from India to Ethiopia — the same provinces Mordecai's letters reach.

Esther 1:22 describes a royal letter sent to all provinces — a parallel administrative action to Mordecai's letters here.

Esther 3:12 records Haman's decree sent to all provinces — the same network Mordecai uses for his counter-decree.

Esther 8:9 describes Mordecai's earlier letter authorizing self-defense — the same administrative process repeated here for Purim.

Exodus 17:14 commands writing a memorial against Amalek; Mordecai's letter establishing Purim fulfills that pattern against Haman, an Agagite.

2 Chronicles 30:5 records a proclamation for Passover observance — a parallel to Mordecai's letters establishing Purim.

Jeremiah 29:1 describes a letter sent to Jewish exiles in Babylon — a parallel to Mordecai's letters to Jews across the empire.