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Glossary

Suppression list

A suppression list is the set of addresses you must never email again: people who opted out, addresses that hard-bounced and anyone else you have promised to leave alone.

Updated · By Otman Ounana · How we research

Why it matters when you send from your own Gmail

The law sets a deadline for honouring an opt-out, and in the US it is 10 business days.[1] Google recommends fulfilling unsubscribe requests within 48 hours.[2] The practical answer is immediately and automatically. In Honest Intros each account has its own list. A one-click unsubscribe, an opt-out reply and a hard bounce each add the address, and nothing is sent to a listed address, including in the next campaign.

Example

A prospect clicks Unsubscribe in Gmail. Their address goes on the list at once. Three months later a new campaign includes their company, and the email to that address is not sent.

What to do

Check that opt-outs reach the list automatically, and never remove an address from it to make a campaign bigger. If you also keep another list elsewhere, copy opt-outs across by hand.

Related terms

All terms are on the glossary.

Read next

  • How fast to honour "remove me"The deadlines for honouring an unsubscribe or "remove me" reply after a cold email: UK, EU, US and Canada, quoted from the regulators and the laws, plus Gmail and Yahoo.
  • One-click under 5,000 a dayGoogle's one-click unsubscribe rule starts above 5,000 messages a day. What still applies below that, what the law asks for, and why a one-click link is worth adding anyway.
  • List-UnsubscribeList-Unsubscribe is an email header that carries an unsubscribe address, so a mail app can show its own Unsubscribe button without the recipient opening the message.
  • CASLCASL is Canada's Anti-Spam Legislation, a consent-based law that prohibits sending a commercial electronic message unless the recipient has consented, expressly or by implication.

Sources

  1. US Federal Trade Commission, CAN-SPAM Act: A Compliance Guide for Business. “You must honor a recipient’s opt-out request within 10 business days.” Read on 1 October 2026.
  2. Google, Email sender guidelines FAQ. “To reduce spam reports, protect your sending reputation, and keep your email lists healthy, we recommend that you fulfill unsubscribe requests within 48 hours, a reasonable timeline for removing recipients from a mailing list.” Read on 1 October 2026.