--- title: "What is a suppression list?" description: "A suppression list is the set of people and addresses you must never mail. Learn why it matters in B2B direct mail and how to keep one clean." canonical: https://trysincerely.com/glossary/suppression-list last_updated: 2026-08-18 --- # What is a suppression list? > A suppression list is the set of people and addresses you must never mail. Learn why it matters in B2B direct mail and how to keep one clean. Source: https://trysincerely.com/glossary/suppression-list A suppression list is the set of contacts and addresses you exclude from every mailing, no matter what. People land on it because they asked you to stop, because they are customers in an active deal you should not confuse, or because their address bounced as [return to sender](https://trysincerely.com/glossary/return-to-sender). Before a campaign prints, you check every recipient against the list and drop the matches. ## Why it matters Email has an unsubscribe link. Mail does not. When someone asks you to stop mailing them and another postcard shows up six weeks later, you look careless at best and hostile at worst. In B2B that reputation cost is concentrated: the person you annoyed sits on a buying committee you care about. A suppression list also protects your budget. Every suppressed piece is a piece you did not pay to print and post. Mailing a churned customer a "welcome" offer wastes money and goodwill in one stroke. The common failure is lag. The opt-out lives in a spreadsheet, the campaign pulls from the CRM, and the two sync monthly. Suppression only works when it applies at print time, not at list-build time. In Sincerely, suppression is immediate and global: suppress a contact once and no campaign in the workspace can mail them again. Suppression is one input to overall [mailability](https://trysincerely.com/glossary/mailability), alongside address quality checks like [NCOA](https://trysincerely.com/glossary/ncoa). ## Example You run a 500-piece campaign to closed-lost accounts. Your suppression list holds 14 entries: 9 people who asked to stop, 3 addresses that bounced, and 2 accounts now in active deals. The check removes 11 recipients from the run. You mail 489 pieces and nobody who said no hears from you. A suppression list is a promise: when someone says stop, you stop, everywhere, forever. --- 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.