A list of 50,000 contacts can contain mistyped addresses, closed mailboxes and temporary accounts. Checking the list before a campaign helps you avoid spending time and sending capacity on contacts you cannot reach. The practical challenge is processing it reliably and deciding what to do with each result.
Prepare the list before you upload it
Keep the original export, remove duplicate addresses and retain the fields that let you connect each result to your CRM. Confirm that you have permission to contact the people on the list. A deliverable address does not establish consent.
ByeBouncer accepts CSV, TXT and XLSX files in the dashboard, with up to 5,000 unique emails per job. A list of 50,000 therefore needs at least ten batches. Submit them within your account balance and active job limits; starting every batch at once does not guarantee earlier completion.
Use a background job for large lists
Bulk verification continues in the background while you follow progress in the dashboard. API integrations can use an idempotency key when creating a job to help prevent duplicate submissions after a network retry. Record the job ID so you can retrieve its status and results.
Credits are reserved when the job starts. Unprocessed work is refunded according to the job accounting rules. If you cancel a job, review the processed and refunded totals rather than assuming that the entire submission was free.
Allow time for domain limits
A list concentrated on a few domains may take longer than a diverse list of the same size. Temporary deferrals, server timeouts and domain limits can leave some checks inconclusive. Increasing concurrency indiscriminately can create more deferrals.
For illustration, processing 5,000 addresses under a hypothetical limit of five checks per minute takes about 16 hours and 40 minutes before retries. This is arithmetic, not a completion estimate for your job. Use the live progress estimate and leave a buffer before your campaign deadline.
Turn the results into a sending decision
- Valid: use the result with your consent, engagement and suppression records.
- Invalid: remove or correct the address before sending.
- Risky: review the reason, such as a disposable or catch-all domain.
- Unknown: keep separate for a later check or review; do not treat uncertainty as proof of validity.
Download the completed CSV before its seven-day availability window ends. Store the results in your own system if you need a longer audit trail. Signed download links are temporary, so retrieve a fresh link from the job when necessary.
Verification is one part of deliverability
List quality, authentication, consent, complaint rates and sending patterns all affect a campaign. Verification cannot promise zero bounces or inbox placement. Read our guide to inconclusive mailbox checks, then create an account to try the workflow on a small sample.
Further reading: Google email sender guidelines and SMTP specification, RFC 5321.