Before you connect an email verification API

Getting a successful API response is the easy part. Decide what your application should do when it doesn't get one.

Keep these cases separate:

• The address was checked and a usable result came back.
• The check finished without a conclusion.
• The request failed, so you don't know whether the check ran.

An authentication error is a problem with your integration. A timeout is a problem with the request completing. Neither means the user's email address is invalid.

Keep API keys on the server. Use the current documentation for authentication, request formats, rate limits and any retry rules. Don't build around an example copied from an old announcement.

Save enough to use the result correctly

Store the checked address, the outcome, the relevant reason and when the check happened. Keep subscription preferences in separate fields.

If a user changes their address while a background check is running, make sure the old response cannot mark the new address as verified. Match the result to the exact version of the address you submitted.

Choose a timeout that fits the workflow. A signup page needs to respond promptly; a background import can wait longer. Decide how unresolved checks will be reviewed, and cap retries so an outage doesn't become a stream of repeated requests.

For a recurring import, test the whole round trip on a small file: submission, result handling, exclusions and writeback. Include an inconclusive result and a failed request. Those cases tell you more about whether the integration is ready than another successful check.