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What is an email suppression list?

Also called: do-not-email list, opt-out list

A suppression list is the set of email addresses you must never send to, such as people who unsubscribed, addresses that hard-bounced and people who marked your email as spam. It should apply across every tool and campaign you send from.

By John Britton, VP of Marketing, MedicalProspects · Updated November 4, 2026 · Compliance

Why it matters for healthcare sales and marketing

Honoring opt-outs is required by CAN-SPAM and similar laws, and mailing bounced or complaining addresses damages your reputation. Most failures happen when opt-outs live in one tool but another tool keeps sending.

How it works

  • Include: unsubscribes, hard bounces, spam complaints, and anyone who asked not to be contacted.
  • Apply everywhere: CRM, marketing automation, sales engagement and any agency sending for you.
  • Apply to new lists: suppress every purchased or imported list before the first send.
  • Don't sell or share opt-outs except to make sure they are honored.
Suppression list sources (unsubscribes, hard bounces, complaints, do-not-contact requests) feeding one central list applied to CRM, marketing automation, sales engagement and new lists.
Keep one central suppression list and apply it to every tool and every new list.

Example

Illustrative scenario. Before loading a new list of hospital executives, a Marketing Ops manager runs it against the company's central suppression list. Several hundred contacts who had previously opted out are removed before any email goes out.

Common mistakes

  • One suppression list per tool. Centralize it.
  • Forgetting agencies and partners. They must apply your suppressions too.
  • Not suppressing new lists. Purchased data can include people who opted out before.

How MedicalProspects does it

MedicalProspects can apply your suppression file before delivery, so opted-out contacts and current customers are removed from your list.

Related terms

  • CAN-SPAM ActThe CAN-SPAM Act is the U.S. law that sets the rules for commercial email, including business-to-business email. It doesn't require prior consent, but it does require honest sender information and subject lines, a physical postal address, a working opt-out, and handling opt-outs within 10 business days.
  • Opt-In and Opt-Out (Email Consent)Opt-in means a person agrees before you email them; opt-out means you may email them until they ask you to stop. U.S. law (CAN-SPAM) is an opt-out system, while Canada's CASL is largely opt-in and the UK and EU have their own rules.
  • Bounce Rate (Hard and Soft Bounces)Bounce rate is the share of sent emails that were returned as undeliverable. Hard bounces are permanent failures, such as an address that doesn't exist; soft bounces are temporary, such as a full mailbox or a server that is briefly unavailable.
  • Sender ReputationSender reputation is how mailbox providers such as Gmail and Outlook judge the trustworthiness of your sending domain and IP addresses, based on signals like spam complaints, bounces, spam trap hits, engagement and authentication.
  • Custom List BuildA custom list build is a contact list assembled to your exact specification, combining criteria such as specialty, role, care setting, geography and technology, instead of buying a ready-made list as is.

Put it to work

Sources

  1. CAN-SPAM Act: A Compliance Guide for Business, Federal Trade Commission

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