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Transactional email API
An email suppression list is the set of addresses you must never send to again: people who unsubscribed, addresses that hard-bounced, and anyone who asked to be erased. Warmerly keeps one per workspace, adds unsubscribes and bounces automatically, and audit-logs every removal.
An opt-out applies to you, not to one campaign. A suppression list scoped to a single campaign means the same person is contacted again the moment someone builds a new sequence — which is both a legal problem and the fastest way to collect spam complaints from exactly the people most inclined to file them. Warmerly suppresses at the workspace level, so an opt-out holds across every campaign, every sender and every channel.
Unsubscribes and hard bounces are added the moment they happen, with the reason recorded. You can also paste addresses in by hand — a client's employees, a competitor, a domain you have agreed not to approach — and those are tagged as manual so the distinction between 'they asked' and 'we decided' is never lost.
Adding an address to a suppression list is safe. Taking one off is the action that can put you back in front of someone who asked you to stop, and it is the action a regulator will ask about. Every removal is recorded with the actor and the timestamp, so the answer to 'who un-suppressed this address' exists before anyone needs it.
Suppression is the least interesting feature in any outreach tool and the one that decides whether the rest of it is legal. It is also where most tools quietly cut corners — scoping the list per campaign, forgetting to suppress on bounce, or letting a send proceed when the compliance data is missing. This page is about doing the boring thing correctly.
An email suppression list is a list of addresses your sending tool checks before every send and refuses to email, whatever list, segment or campaign they turn up in later. It is how an opt-out keeps working after the campaign it came from has ended. In email marketing and cold outreach alike it holds the same four kinds of address, and the rule is always the same: an address on the list is skipped, not deleted, so the record of why it is there survives.
Where the list lives matters as much as what is on it. Email marketing platforms such as Campaign Monitor keep one per account or client, and it only protects sends that go through that platform. If you run cold outreach from a second tool, its suppression list starts empty. So when you move tools, export the old suppression list and import it before the first send (see 'Importing an existing suppression list' below).
Mailbox providers only report spam complaints to senders enrolled in a feedback loop, which bulk email platforms are and Gmail or Microsoft 365 mailboxes sending cold outreach are not. So Warmerly cannot see a complaint made against cold mail and cannot suppress it automatically. Add anyone who complains by reply as a manual entry. On Warmerly's transactional API, which sends through Amazon SES, complaints are reported and suppressed automatically.
Three things, in ascending order of cost. First, complaints: people who asked to be removed and were contacted again are the population most likely to hit 'report spam' rather than unsubscribe a second time, and complaint rate is the single most damaging deliverability signal there is.
Second, blocklisting: repeated sending to hard-bounced addresses is a strong signal that you are working from a stale list, and stale lists are how domains meet spam traps. Third, regulatory exposure. Under GDPR and PECR an objection to direct marketing must be honoured, and under CAN-SPAM an opt-out must be processed within ten business days and then respected indefinitely. 'It was a different campaign' is not a defence in any of those regimes.
A hard bounce is a definitive statement from the receiving server that the mailbox does not exist. Sending to it again produces another hard bounce, and a sender whose bounce rate stays elevated is telling every provider it is not maintaining its list. Bounce rate feeds reputation directly, and it is one of the fastest ways to lose placement on a domain that was otherwise healthy.
Soft bounces are different — a full mailbox or a temporary server problem is not a permanent fact about the address — and they are not treated the same way. The distinction matters, because suppressing every soft bounce would quietly delete a slice of your reachable audience over time.
Suppression catches the bounces you have already paid for. Verification stops most of them ever happening. The two are complementary, and running only the second one means learning your list is dirty by damaging your domain with it.
CAN-SPAM requires a valid physical postal address in commercial email. It is not optional, it is not decorative, and the absence of one is among the easiest violations to prove because it is visible in the message itself.
Warmerly will not send a campaign from a workspace with no postal address on file. Not a warning banner, not a nag — the send is blocked. This is deliberately inconvenient, and it was made deliberately inconvenient after an audit found that essentially no workspace had filled the field in. A soft requirement that everybody ignores provides compliance theatre rather than compliance.
An opt-out is only meaningful if using it is easier than reporting spam. Warmerly's unsubscribe links are signed, so they cannot be forged or enumerated, and they take effect immediately on click — the address is on the suppression list before the confirmation page finishes rendering, with no login, no preference centre and no 'we'll process this within ten days'.
This is self-interested as well as correct. Every unsubscribe you make easy is a spam complaint you did not receive, and a complaint costs your domain far more than a lost contact does.
If you are moving from another tool, bring the list with you before your first send. Paste the addresses in or upload a CSV column; a header row is ignored. Entries added this way are marked manual, which is honest — the system knows you supplied them, not that it observed the opt-out itself.
This is the single most important migration step and the one most often skipped, because nothing breaks when you skip it. What happens instead is that everyone who opted out of your last tool receives your first campaign from the new one.
The whole list exports to CSV with reasons and dates. Suppression data is the record of who told you to stop, and it needs to be portable — for migrating to another tool, for handing to a client at the end of an engagement, and for producing evidence if anyone ever asks you to demonstrate that an objection was honoured.
It is the list of addresses your email platform will never send to again: people who unsubscribed, addresses that hard-bounced, people who marked you as spam, and anyone you have been legally asked to stop contacting. The platform checks every send against it, so an opt-out keeps working in every later campaign.
An unsubscribe list holds only the people who opted out. A suppression list is broader: it also holds hard bounces, spam complaints and manual or legal entries. Everyone on an unsubscribe list belongs on your suppression list, but not the other way round.
No. If you delete an address, the record that it must not be emailed goes with it, and the next import of an old list brings it straight back. Keep it suppressed. The suppression entry is also your evidence that an opt-out was honoured.
Yes — it is workspace-wide. An opt-out applies to the sender, not to one sequence, so it holds across every campaign and every channel in that workspace.
Yes, along with hard bounces, at the moment they occur and with the reason recorded. You do not need to import anything or run a sync.
You can, and every removal is written to the audit log with who did it and when. Be certain before you do — an address on that list is usually there because a person asked for it to be.
The most common reason is that the workspace has no postal address on file, which is a hard block rather than a warning. The launch-readiness panel on the campaign names the blocking check.
Yes. The obligation to honour an opt-out does not expire with your subscription. Export the list to CSV before you leave and carry it into whatever you use next.
Workspace-wide suppression, automatic on unsubscribe and bounce, audit-logged on removal — from your first campaign, not as an upgrade.