Entries land on a do-not-contact list four ways. Someone clicks unsubscribe. An address hard-bounces, proving it is dead — trying it again only damages your sender reputation. A recipient marks a message as spam, which is a stronger signal than an unsubscribe and should be treated as permanent. Or you add contacts yourself: current clients who should never get a cold pitch, prospects who said no last quarter, a competitor's domain.
The phrase "enforced at send time" is what separates a real suppression list from a spreadsheet of good intentions. A list that is only consulted when a campaign is built leaks constantly: a suppressed contact gets re-imported from a fresh lead source, or a draft written on Monday goes out on Thursday to someone who unsubscribed on Tuesday. The check has to happen at the moment of sending, on the server, where no workflow can route around it. In Brohns the do-not-contact list works exactly this way — every message, including one you have already approved, is checked against the list as it goes out, alongside the daily send limit and the send window, and hard bounces are added automatically so a dead address is never tried twice.
Suppression also pairs naturally with human review. In Brohns, an agent's outreach drafts queue up for your sign-off before anything sends, so you see exactly who is being contacted — the do-not-contact list is the backstop underneath that review, catching what a busy reviewer might miss. Every outgoing email carries a one-click unsubscribe link, and honoring those clicks is automatic rather than a weekly cleanup chore. Seed the list before your first campaign with existing customers, past decliners, and anyone who has ever asked to be left alone: the fastest way to burn a small niche is messaging someone twice who said no once.