Duplicate Prevention
Duplicate Prevention is an automatic safety mechanism that skips a mail piece if the same recipient address appears in a new order within 36 hours of a prior send. This protects against accidentally mailing the same person twice in rapid succession.
You can disable Duplicate Prevention for your account in Mail Preferences (gear icon ⚙ in the top navigation bar), under the Duplicate Prevention section.
How it works
When you place an order or a campaign fires a send, thanks.io checks whether each recipient address was already sent to in the past 36 hours. If it was, the duplicate piece is skipped for that order.
The 36-hour window is per-recipient address, not per-campaign or per-list.
What Duplicate Prevention does not cover
Duplicate Prevention governs mail sends. It has no effect on buying data, so it does not stop you paying twice for the same mailing list records.
Duplicate Radius Search purchases are handled by a separate check: an identical Radius Search purchase from the same account is refused within 24 hours of the first one, and the response hands back the mailing list ID (and order ID, where the search was bought as part of an order) from the original purchase. See Duplicate purchase protection.
| Duplicate Prevention | Duplicate Radius Search purchases | |
|---|---|---|
| Stops | Mailing the same person twice | Buying the same leads twice |
| Window | 36 hours | 24 hours |
| Compares | Recipient address | Search parameters, and the order when the search is part of one |
| Configurable | Yes, in Mail Preferences | No, always on |
The one exception: Gift Cards
Duplicate Prevention cannot be disabled for Gift Cards. Regardless of your account setting, Gift Cards always observe the 36-hour window.
All other mailer types - postcards, letters, Notecards, MagnaCards - respect your account setting.
When this affects you
- If you upload the same list to two campaigns that fire close together, some recipients may be skipped on the second send.
- If you manually add a recipient to a list while a campaign is already running for that same address, the recipient may be skipped.
- If you test with your own address repeatedly, you'll hit the 36-hour window and the send will be skipped.
Tips & best practices
- Wait at least 36 hours between test sends to the same address.
- If you're intentionally sending a second piece to the same list quickly (e.g., a follow-up the next day), be aware those recipients will be skipped - use separate timing or disable Duplicate Prevention in settings.
- Use separate lists for campaigns that should mail to the same recipients on different days.
Limits & gotchas
- Duplicate Prevention applies on all tiers.
- The window is 36 hours - not 24 hours. The 24-hour window belongs to duplicate Radius Search purchases, which is a different check.
- Skipped pieces are not queued for later - they are dropped from that order entirely.