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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.

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.
  • Skipped pieces are not queued for later - they are dropped from that order entirely.