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CampaignsBeginner2 min readUpdated 22 August 2026

Preparing a contact list: E.164, deduplication and cleaning

How the importer reads your file, what E.164 means, why duplicates are merged, how invalid rows are reported, and how to keep a list healthy over time.

Part 3 of 4 in the path Your first week

Files the importer reads

CSV, TXT and XLSX, up to 50 MB per file, with or without a header row. The first column that looks like phone numbers is used as the destination; every other column becomes a variable you can use in the text, such as {first_name}. Paste a list directly if it is short.

E.164 in one minute

E.164 is the international format: a plus sign, the country code, the national number without the trunk zero, no spaces. +44 7700 900123 becomes +447700900123. It is the only format carriers understand, and the only one that tells us which country's rate and rules apply.

What normalisation does

Numbers in local format are converted when the country is known: set a default country for the file, or add a country column. Spaces, dots, dashes and parentheses are stripped. A leading 00 is treated as the plus sign. Numbers that still cannot be resolved, too short, too long, unknown prefix, are excluded and listed, never sent, never billed.

Deduplication

The same number written two ways is one recipient. After normalisation, duplicates are merged and the first row's variables are kept. The import report says how many were merged so you can check the source when the count surprises you.

The import report

Rows read, rows ready, invalid rows with the reason, duplicates merged, destinations found with a count per country and the cost split at current rates. Read it before composing: a list that turns out to be 40 % Brazil needs a numeric sender strategy that a European list does not.

Keeping a list healthy

  • After each campaign, remove numbers reported as unknown. The report has a one-click action for it.
  • Keep opt-outs; they are excluded from future sends to that list automatically, but you should also stop collecting them elsewhere.
  • Store the consent source with each number.
  • Re-check dormant lists with a small transactional send before a large campaign.

Message history is kept for 90 days, long enough to compare two campaigns to the same list and see whether it is ageing.

Put it into practice.An email address opens the account. Rates are public, payment is crypto, and the test key is free.
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Something unclear or out of date? Write to [email protected]; corrections are folded back into the guide and the update date changes.