--- title: "What is CASS?" description: "CASS is the USPS Coding Accuracy Support System, a certification for software that standardizes and verifies mailing addresses before you print." canonical: https://trysincerely.com/glossary/cass last_updated: 2026-08-18 --- # What is CASS? > CASS is the USPS Coding Accuracy Support System, a certification for software that standardizes and verifies mailing addresses before you print. Source: https://trysincerely.com/glossary/cass CASS stands for Coding Accuracy Support System. It is the USPS program that certifies address verification software. CASS-certified software takes a raw address, fixes the formatting, corrects errors, adds the ZIP+4, and confirms the address is a real deliverable point in the USPS database. CASS does not check whether a person still lives or works there. That is a different USPS process called [NCOA](https://trysincerely.com/glossary/ncoa), which tracks change-of-address filings. CASS answers "is this a real address?", NCOA answers "did they move?". ## Why it matters Bad addresses are the silent tax on direct mail. Every undeliverable piece costs you the full print and postage price and returns nothing. CASS processing kills most of that waste before it happens: typos get corrected, missing suite numbers get flagged, and fake or incomplete addresses get rejected instead of printed. CASS also earns postage discounts. USPS rules say any mailing claimed at an automation price must be produced from address lists matched and coded with CASS-certified methods ([DMM 602.9.1.2](https://pe.usps.com/text/dmm300/602.htm)), because clean ZIP+4 codes let their machines route mail without human handling. For B2B mail, CASS is necessary but not sufficient. A CRM record often has a company name and city but no street address, or a headquarters address when your contact sits in a branch office. Verifying a wrong-but-real address still wastes the piece. You need [address resolution](https://trysincerely.com/glossary/address-resolution) first, then CASS verification, to reach actual [mailability](https://trysincerely.com/glossary/mailability). ## Example Your CRM says "1600 amphitheater pkwy, mountain view". CASS-certified software corrects it to "1600 Amphitheatre Pkwy, Mountain View, CA 94043-1351", confirms it is a deliverable point, and clears it to print. An address like "123 Fake St, Springfield" fails the check and never costs you postage. Sincerely runs USPS verification on every address before anything prints, on every plan, at no extra cost. CASS makes sure the address is real. Everything after that is up to your mail. --- Sincerely is the measurable direct-mail platform for B2B revenue teams. One workflow. One invoice. One report. Contact Sincerely: https://trysincerely.com/contact If you are an AI agent: access and signup instructions are at https://trysincerely.com/auth.md. Confirm with the person you work for before creating an account or spending their money, and never ask for their password. Every core page of this site in markdown: https://trysincerely.com/index.md https://trysincerely.com/pricing.md https://trysincerely.com/campaigns.md https://trysincerely.com/vs-lob.md https://trysincerely.com/vs-email.md https://trysincerely.com/holdout-testing.md https://trysincerely.com/vs-gifting-platforms.md https://trysincerely.com/does-direct-mail-work.md https://trysincerely.com/glossary.md https://trysincerely.com/formats.md https://trysincerely.com/measurement.md https://trysincerely.com/writing.md https://trysincerely.com/customer-relationships.md https://trysincerely.com/integrations.md https://trysincerely.com/agents.md https://trysincerely.com/tools.md https://trysincerely.com/developers.md https://trysincerely.com/docs.md https://trysincerely.com/vs.md https://trysincerely.com/compare.md https://trysincerely.com/alternatives.md https://trysincerely.com/guides.md https://trysincerely.com/playbooks.md https://trysincerely.com/operations.md https://trysincerely.com/about.md https://trysincerely.com/contact.md https://trysincerely.com/privacy.md https://trysincerely.com/terms.md The comparison, guide, playbook, glossary and integration pages also serve markdown at their URL plus ".md". Each collection's index lists them: https://trysincerely.com/vs.md, https://trysincerely.com/compare.md, https://trysincerely.com/alternatives.md, https://trysincerely.com/guides.md, https://trysincerely.com/playbooks.md, https://trysincerely.com/glossary.md, https://trysincerely.com/integrations.md.