Verification at the ecommerce checkout
In ecommerce the address is not a marketing asset first. It is where the order confirmation goes, where the shipping notification goes, and where the return label goes when something is wrong.
A mistyped address at checkout produces a customer who paid, received nothing, and contacts support convinced the order failed. The refund is usually cheaper than the review.
The typo is worth more than the dead address
Checkout typos cluster in predictable places: gmial.com, yaho.com, hotmial.com, a missing letter in the local part. Each one is a paid order whose confirmation bounces.
That is why the response carries a did_you_mean field when the domain is one edit away from a common provider. Showing the suggestion on the page while the customer is still there costs one support ticket less than finding out afterwards.
Never apply the correction automatically. Some people genuinely use unusual domains, and silently rewriting an address is how an order confirmation goes to a stranger.
How the work gets done
The order that matters for ecommerce, rather than a generic checklist.
Check on field blur, not on submit
The customer has typed the address and moved on, so there is a moment to use. Checking at submit adds latency to the step where abandonment is most expensive.
Suggest, never correct
Show did_you_mean as a question the customer can accept or dismiss. An automatic rewrite sends the receipt somewhere else and nobody finds out for a week.
Fail open, always
A two-second timeout and a timeout counts as a pass. A verifier having a slow moment must never be the reason a paid order does not complete.
Verify the marketing list separately
Checkout is a real-time single check. The newsletter list is a batch job, and treating them as the same problem gets you a slow checkout and an unverified list.
What verification will not do here
What it costs
At $5 per thousand addresses, a checkout check costs half a cent. Against a mis-delivered order and a support contact, the arithmetic is not close.
Every tier works the same way. Unknown results and duplicates are never billed, and credits do not expire.
Questions we get asked
Will this slow down my checkout?
By the timeout you set, at most, and only if we are slow. Check on blur with a two-second budget and treat a timeout as a pass.
Should I block disposable addresses at checkout?
Rarely. In signup abuse the case is strong. At checkout, someone with a card in hand is a customer whatever mailbox they used.
How do I handle the Shopify side?
The integration page covers it: a theme-level check on the field and a batch job for the customer list, which are two different problems.
Try it on your own list first
100 free checks a month, no card. Run a sample and read the unresolved count before you decide anything.