Email Deduplication Window

Definition

An email deduplication window is the time period used to determine whether two or more records of the same email address are treated as duplicates. Within the window, repeated appearances of an address — such as multiple signups, imports, or engagement events — are collapsed into a single subscriber rather than counted separately. The window matters because it defines how aggressively a sender removes redundancy and how much behavioural history is preserved.

How It Works

Deduplication compares addresses against the existing list to decide whether a new record is genuinely new or a repeat. The deduplication window sets the horizon over which that comparison is meaningful.

• Window definition — the window specifies a time frame, such as 90 or 180 days, during which duplicate events are merged.
• Match detection — incoming addresses are matched against existing records, and matches within the window are treated as the same subscriber.
• Merge or skip — matched records are either merged into the existing profile or skipped, depending on whether the new event carries useful data.
• Window expiry — after the window closes, old duplicates are no longer actively consolidated, which can affect how historical behaviour is counted.

The choice of window reflects a trade-off. A long window removes more duplication but risks merging genuinely separate interactions, while a short window preserves detail but allows redundancy to persist.

Best Practices

• Align the window with your sales cycle — for most senders, 90 to 180 days balances deduplication against behavioural detail.
• Use address normalisation first — lowercase the local part and strip plus-tags so variants of the same address are correctly matched.
• Keep consent records intact — deduplication should merge behaviour, not erase email-consent evidence.
• Apply deduplication consistently — the same window should govern imports, signups, and list merges so results are comparable.
• Review the window periodically — as behaviour and sending cadence change, the ideal window may shift.

Example

A brand sets a 120-day deduplication window. A subscriber signs up in March and signs up again in June. Because the second signup falls within the window, the two records are merged into one profile with both signup sources noted. A further signup in November falls outside the window and is treated as a fresh event, triggering a new review rather than an automatic merge.