From Squarespace to Brevo.
When we rebuilt the Court House Farm website, their mailing list came with it. We moved every contact out of Squarespace and into Brevo, split them into lists like retreat enquiries, past buyers and general subscribers, and carried every unsubscribe across as a blocklist so nobody who'd opted out was emailed again.
The same move brought their past orders and customers across into the new shop.
See the website we built