If you also run WP Conversion Tracker or Launch Manager, the mailer can read their data. That is useful, because it fills in names, countries and purchase history for people you already have.
It also means historical tracker and buyer records can become subscribers in their own right, which is not always what you want.
Settings has an option called Only create people from direct sign-ups, sales and imports.
With it on:
- The tracker and buyer syncs still enrich people you already have.
- They can no longer add somebody new.
Not affected by this setting:
- Somebody filling in one of your forms
- A sale
- A CSV import
- Adding somebody by hand
The option is off by default, so nothing changes unless you turn it on.
If you have deleted records and they came back, this is why: the sync runs every hour. Turn this option on and they stay deleted.