The new email is saved on the order, so Shopify's order and shipping updates go to the new address from then on. And, by default, Tacey sends a short security notice to the old address, so if anyone other than the real customer made the change, the real customer finds out.
Why the old address gets a notice
The order status page can be reached from an order link, not only from a signed-in account. If someone got hold of that link and changed the email, the real customer would stop receiving updates about their own order and might never notice. A notice to the old address closes that gap: an unexpected change is never silent.
What the notice says
It comes from your store (your sender name), not from Tacey. It reads:
Subject: Your email on order #1001 was changed
Body: The email on your order #1001 with [your store name] was just changed to j•••@example.com. If this wasn't you, reply to this email and we'll look into it.
The new address is partly hidden (only its first letter and the part after the @ are shown), so the notice never hands a full email address to whoever reads the old inbox.
If you also update customer accounts (the Also update the customer's account setting) and the account's sign-in email was different from the order's, the account's previous email gets the same notice too. One inbox never receives two copies.
Replies go to your Customer support email, set in Editing Tools, then Global settings, under Sender identity. The tool's settings page shows which address that currently is.
Why you cannot edit the wording
This is a security message. If its wording could be changed, it would be easier to make an unwanted change look routine. So the text is fixed. It is sent in the customer's language when Tacey knows it, otherwise in your store's language.
The setting
Email the old address when the email changes is on by default.
In Tacey, open Editing Tools.
Open Update contact details and click Configure.
Tick or untick Email the old address when the email changes.
Click Save.
Leave it on unless you have a strong reason. It costs your customers nothing and it is the main protection against someone else redirecting an order's emails.
What else happens on the order
The order's history in Tacey records Contact details changed, with the before and after values and that the customer asked for it.
The change counts as one of the customer's allowed changes on that order.
If you turned on Email me when a customer changes their contact details, you also get a short summary. See How do I get an email when a customer changes their contact details?.
What this does NOT do
It does not send a confirmation to the new address. The only automatic email is the security notice to the old one.
It does not ask the customer to verify the new address with a code. Tacey checks the email is correctly formed (and, if you choose, not a disposable inbox), but does not confirm ownership.
It does not change the email the customer signs in with unless you turn on Also update the customer's account.
It does not send a notice when only the phone number changes.
Frequently asked
A customer says they got an email about a change they did not make. What do I do?
Open the order in Tacey to see the change in its history, then contact the customer at their original address and change the email back yourself in Shopify admin. Consider adding a blocked tag to the order while you look into it.
The customer removed their email entirely. Does the old address still get a notice?
Customers can only remove their email if you turned on Let customers remove their email or phone entirely, and Tacey only sends the notice when there is a new email to report.
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