This account's mail preferences and the address they apply to

Read the preference row, creating it on this first read if need be.

The row is minted lazily rather than backfilled by the migration for the reason email/preferences.py gives: a backfill would write a bearer token for every account that predates the table, most of which will never receive a marketing mail. So a read is a write, exactly once, and the column defaults are what a missing row already meant.