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Mailing Guides

Preparing a Mailing List

How to format a mailing list, why CASS and Move Update matter, deduplication and householding, and what drives the price your list qualifies for.

Reflects USPS standards effective 2026-07-12, as loaded in our production system.

How should I format a mailing list file?

Provide the list as a spreadsheet (CSV or Excel) with clear, separate columns: full name, company (if any), address line 1, address line 2/suite, city, state, and ZIP. Keep one record per row and consistent headers. Avoid merged fields and stray formatting. Plavidian standardizes the file during processing.

CASS and ZIP+4

CASS processing standardizes each address, validates it, and appends the ZIP+4 and delivery point needed for a valid barcode and automation prices. Addresses that fail CASS cannot claim automation and may be undeliverable. See What is CASS processing and why does it matter and ZIP+4 and delivery point.

Move Update

Presort and automation mailings must be Move-Update compliant (commonly NCOALink) within 95 days of mailing, which updates addresses for people who have moved. See What is the Move Update requirement.

What are deduplication and householding?

Deduplication removes repeated records so you do not mail the same person twice. Householding combines multiple recipients at one address into a single piece where appropriate. Both cut waste and postage. Plavidian can dedupe and household during processing.

How many records do I need for bulk prices?

Presort and bulk prices need minimum volumes (First-Class 500 pieces; Marketing Mail 200 pieces or 50 pounds; see How many pieces do I need for presort pricing). How deeply a list sorts, and therefore how low the price goes, depends on how the records concentrate into ZIP areas, which the software determines at processing. Run the list through Mailing Analysis to see what it qualifies for.

Seed addresses

Seed or decoy addresses added to the list let you and Plavidian confirm pieces actually landed and gauge the in-home window. Recommended for larger campaigns.

House vs acquired lists

A house list (your own customers) usually responds best and is cleanest. Rented or acquired lists reach new prospects but need the same CASS and Move Update processing and vary in quality. For saturation of an area with no list at all, use EDDM (see What is EDDM).

Have a question this guide does not cover?

Ask the Plavidian Mail Expert and get an answer grounded in the USPS Domestic Mail Manual, or send us your piece and we will confirm it before you print.

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More mailing guides

USPS Mail Classes Explained

First-Class, Marketing Mail, Nonprofit, Bound Printed Matter, and Media Mail: what each class is for, what it can contain, and how to choose.

Postcard, Letter, Flat, or Parcel: USPS Size Limits

The exact dimensions that decide whether your piece prices as a postcard, letter, flat, or parcel, plus the nonmachinable surcharge list.

Folded Self-Mailers and Tabbing Requirements

How many tabs a folded self-mailer needs, where they go, fold orientation, paper weight minimums, and when tabbing does not apply.

Mailing Booklets: Size, Spine, and Tabbing Rules

How a bound booklet mails: letter versus flat thresholds, spine orientation, tab count by weight, and paper stock minimums.

Automation and Presort: How to Earn the Lowest Postage

What machinable, nonmachinable, and automation mean, the presort minimums, and the requirements that unlock the lowest per-piece prices.

Addressing, CASS, and Move Update Requirements

CASS processing, ZIP+4 and delivery point coding, the Move Update rule, and ancillary service endorsements for undeliverable mail.