An unfinished sending domain cleans itself up
If you add your own sending domain under Integrations and it never gets verified, it’s now removed after 30 days — the Integrations page shows the date while it waits, and you’re emailed when it happens. Nothing that was working stops: receipts, reminders, and sign-in codes keep going out from the included shared address, as they have all along. Add the domain again whenever you’re ready and you get a fresh set of records to hand to whoever manages it.