Keep your agent's mail out of spam traps

Spam traps are the failure mode nobody puts in the demo. A bounce is loud — you get a 5.x.x back, your code logs it, you move on. A complaint at least gives you a webhook. A spam trap gives you nothing. The message gets accepted, no error comes back, and somewhere a mailbox provider quietly writes your domain down as a spammer. By the time you notice, your inbox placement has already cratered and you have no single bounce to point at.

That's the trap, literally. And it's the one that bites autonomous agents the hardest, because the whole appeal of an agent is that it acts without a human watching every send. Point a model at a list it scraped, let it loop, and it'll happily mail a recycled address that's been a trap for two years. The agent never sees a problem. You only see the aftermath in your deliverability dashboard a week later.

I work on the Nylas CLI, so the terminal commands below are the exact ones I reach for when I'm wiring up an Agent Account to not do this. The good news is that an Agent Account is just a grant — a grant_id that works with every grant-scoped endpoint you already know — so there's nothing new to learn on the data plane. The defense is mostly discipline: validate before you send, honor every complaint, and age out the addresses that never wanted to hear from you.

What a spam trap actually is, and why it's not a bounce

It's worth being precise here, because the three things people lump together behave completely differently.

A bounce is a rejected delivery. The receiving server tells you the address is bad, you get a message.bounced event, and you stop. Bounce handling is a solved problem — you listen, you suppress, you're done.

A complaint is a recipient hitting "report spam." The mailbox provider relays that back as a feedback loop, and you get a message.complaint event. The address is real and reachable; the human just doesn't want your mail. If you keep mailing them, you're training the provider to filter you.

A spam trap is neither. It's an address with no human behind it, planted (or recycled) specifically to catch senders who don't manage their lists. There are two flavors:

• Pristine traps — addresses that were never valid and never opted in. Published in places only a scraper would find. If you hit one, it means you're mailing addresses you harvested rather than addresses that gave you consent.
• Recycled traps — addresses that were real, went dormant, bounced for months, and then got reactivated by the provider as a trap. If you hit one, it means you kept mailing an address long after it stopped engaging.

Here's the part that makes traps dangerous: they don't bounce. A pristine trap accepts your mail silently. A recycled trap accepts it too, now that it's live again. There is no Nylas "is this a spam trap" endpoint — there can't be, because the whole point of a trap is that it's indistinguishable from a real inbox until your reputation tanks. So the defense can't be a lookup. It has to be behavior: don't mail addresses you can't trust, and stop mailing addresses that have gone quiet.

That's the honest framing. Everything below is built on it.

What you actually get from Nylas

You don't get a trap detector. You get the two signals that let you build trap avoidance, plus the machinery to enforce a suppression list at the platform edge:

1. Deliverability webhooks — message.delivered, message.bounced, message.complaint, and message.rejected. These tell you what happened to every outbound message. Complaints and bounces are your strongest "stop mailing this person" signals.
2. Lists and Rules — application-scoped suppression. A List holds addresses; a Rule with an in_list condition blocks any outbound send to them; a workspace activates that rule across your Agent Accounts. Once an address is suppressed here, your agent physically cannot email it, even if its own logic slips.

The webhooks tell you who to suppress. The Lists and Rules make the suppression unbreakable. Your application code fills the gap Nylas can't — validating recipients before the first send, and aging out the ones who never engaged.

Let's wire all three.

Before you begin

You need an Agent Account on a registered domain and your API key. If you're starting cold, provision one. The grant it returns is your grant_id for everything after.

curl --request POST \
  --url "https://api.us.nylas.com/v3/connect/custom" \
  --header "Authorization: Bearer <NYLAS_API_KEY>" \
  --header "Content-Type: application/json" \
  --data '{
    "provider": "nylas",
    "settings": { "email": "[e-mail]" },
    "name": "Support Agent"
  }'

nylas agent account create [e-mail] --name "Support Agent"

The API auto-creates a default workspace and policy for the account, which matters later: a suppression rule has to be activated on a workspace, and this is the one your new account already belongs to.

A reminder on message.rejected, because it's easy to misread. That event fires for one specific reason — an outbound message was rejected because an attachment contained a virus. It is not a generic "this send failed" signal and has nothing to do with traps. Subscribe to it for security telemetry, but don't wire it into your suppression logic.

Subscribe to the complaint and bounce webhooks

This is step one of trap defense, because a complaint or a hard bounce is the clearest evidence that an address should never receive another send. Subscribe once, at the application level — Nylas webhooks are app-scoped, not grant-scoped, so a single subscription covers every Agent Account you run. Each payload carries a grant_id you filter on.

curl --request POST \
  --url "https://api.us.nylas.com/v3/webhooks" \
  --header "Authorization: Bearer <NYLAS_API_KEY>" \
  --header "Content-Type: application/json" \
  --data '{
    "trigger_types": [
      "message.complaint",
      "message.bounced",
      "message.rejected"
    ],
    "webhook_url": "https://yourapp.com/webhooks/deliverability",
    "description": "Agent Account deliverability signals"
  }'

Now the honest note you'd want from a colleague rather than a marketing page: you have to create this one through the API, not the CLI. The CLI can absolutely create webhooks — nylas webhook create --url <URL> --triggers <...> — and I use it constantly for message.created and friends:

nylas webhook create \
  --url https://yourapp.com/webhooks/deliverability \
  --triggers message.created

But run nylas webhook triggers and you'll see the published trigger catalog doesn't list the deliverability events. The CLI validates --triggers against that catalog, so message.complaint won't go through the flag today. The POST /v3/webhooks body above accepts them directly. This is the one place in the whole flow where the CLI can't mirror the API, and I'd rather tell you that than have you debug a rejected flag.

When a complaint lands, your handler should do exactly one thing first: add that address to your suppression list. Don't wait for a daily batch — a person who reported you as spam must not receive a second message. Dedupe the webhook itself on the top-level notification id (constant across Nylas's up-to-three retry attempts) so a retried delivery doesn't double-process.

Build the suppression list and the rule that enforces it

A logged complaint that doesn't change behavior is just a sad log line. The enforcement lives in a List plus a Rule, activated on a workspace. This is the part that makes suppression structural rather than a hope that your send loop remembers to check.

First, the list — an address-typed collection. Seed it with the complaining or hard-bouncing addresses as they come in.

curl --request POST \
  --url "https://api.us.nylas.com/v3/lists" \
  --header "Authorization: Bearer <NYLAS_API_KEY>" \
  --header "Content-Type: application/json" \
  --data '{ "name": "Suppressed recipients", "type": "address" }'

nylas agent list create \
  --name "Suppressed recipients" \
  --type address \
  --item [e-mail]

Add to it as complaints arrive — POST /v3/lists/<LIST_ID>/items with an items array, or the CLI's add:

curl --request POST \
  --url "https://api.us.nylas.com/v3/lists/<LIST_ID>/items" \
  --header "Authorization: Bearer <NYLAS_API_KEY>" \
  --header "Content-Type: application/json" \
  --data '{ "items": ["[e-mail]"] }'

nylas agent list add <LIST_ID> [e-mail]

Next, the Rule. It's an outbound rule with one in_list condition against recipient.address, and a single terminal block action. An outbound block rejects the send before it ever reaches the provider — the API returns 403, and no message goes out.

curl --request POST \
  --url "https://api.us.nylas.com/v3/rules" \
  --header "Authorization: Bearer <NYLAS_API_KEY>" \
  --header "Content-Type: application/json" \
  --data '{
    "name": "Block suppressed recipients",
    "trigger": "outbound",
    "match": {
      "conditions": [
        { "field": "recipient.address", "operator": "in_list", "value": ["<LIST_ID>"] }
      ]
    },
    "actions": [ { "type": "block" } ]
  }'

The CLI condenses this into condition-and-action flags:

nylas agent rule create \
  --name "Block suppressed recipients" \
  --trigger outbound \
  --condition recipient.address,in_list,<LIST_ID> \
  --action block

One detail worth knowing: recipient.address matches any recipient on the message — To, CC, BCC, and the SMTP envelope. So a suppressed address hidden in a BCC still trips the block. That's exactly the DLP-grade coverage you want; an agent can't sneak a suppressed contact through on a carbon copy.

Activate the rule — it's inert until you do

This is the step people skip, and then wonder why their block rule does nothing. A rule does nothing until a workspace references it. Creating the rule through POST /v3/rules only defines it. You have to add its ID to a workspace's rule_ids array, and only then does it run for the Agent Accounts in that workspace.

curl --request PATCH \
  --url "https://api.us.nylas.com/v3/workspaces/<WORKSPACE_ID>" \
  --header "Authorization: Bearer <NYLAS_API_KEY>" \
  --header "Content-Type: application/json" \
  --data '{ "rule_ids": ["<RULE_ID>"] }'

nylas workspace update <WORKSPACE_ID> --rules-ids <RULE_ID>

A nice shortcut from the CLI side: nylas agent rule create already attaches the rule it creates to the default workspace for you — that's what "create a rule and attach it to the default agent workspace" in its help text means. So if your accounts live in the default workspace, the CLI path collapses suppression-rule creation and activation into a single command. The explicit workspace update above is what you reach for when you built the rule through the API, or when you're attaching it to a custom workspace. Either way, the principle holds: an unattached rule is a no-op.

With this in place, every complaint your webhook catches flows into the list, and every send the agent attempts to a listed address dies at 403 before it can compound the damage. The platform is now enforcing a boundary your application code can't accidentally cross.

Validate recipients before the first send — this is your job

Here's where I have to be straight with you: everything past this point is your application logic. Nylas doesn't ship a "is this a spam trap" check, and no provider does, because traps are designed to be invisible. The suppression list above handles addresses you've learned are bad. Trap avoidance is about not mailing questionable addresses in the first place.

The single most important rule: never email a scraped, purchased, or old list. Pristine traps live exactly where a scraper would find them. If your agent's input is a list someone harvested, you will hit traps — it's not a question of if. The only addresses safe to mail are ones that asked to hear from you.

Before any first send, run cheap validation in your own code:

• Syntax and domain checks. Reject malformed addresses, and confirm the domain has an MX record before you bother sending. A domain with no MX can't receive mail; sending anyway is wasted reputation.
• Role and disposable filtering. Be wary of info@, admin@, postmaster@ style role addresses on lists you didn't build, and of known disposable-domain providers. Neither belongs in an agent's outreach.
• Consent provenance. This is the one that actually matters. Track how each address entered your system — a form submission, an account signup, a reply to a real conversation. Addresses with no provenance trail are exactly the ones that turn out to be traps.

None of this is a Nylas feature, and I won't pretend it is. It's a validation layer you own, and it's the difference between an agent that builds reputation and one that quietly burns it.

Age out the addresses that never engage

Recycled traps are the slow killer. An address that was real goes dormant, you keep mailing it out of habit, and one day the provider flips it into a trap. The defense is to stop mailing addresses that have gone quiet — before they get recycled.

Use the deliverability webhooks as your engagement ledger. message.delivered confirms a send landed; the absence of any positive signal over time is your aging cue. In your own datastore, track last-engagement per recipient and apply a policy like:

• No opens, clicks, or replies in 90 days? Move them to a re-engagement track — one carefully worded "are you still there?" send, not your normal cadence.
• Still silent after that? Stop mailing them entirely and add them to the same suppression list you built above. A never-engaged address that you keep hitting is a recycled trap waiting to happen.

You can mine engagement signals from the grant-scoped Messages and Threads endpoints the Agent Account already exposes — GET /v3/grants/{grant_id}/messages to see what came back, nylas email list and nylas email read from the terminal when you're spot-checking a thread by hand. There's no special endpoint for this; it's the same data plane every grant has, which is rather the point of the Agent Account abstraction. You're not learning a new API to do reputation hygiene — you're using the one you already have, with discipline.

The shape of the whole defense

Put together, trap defense for an Agent Account is three loops that reinforce each other:

1. Inbound signal — subscribe to message.complaint and message.bounced (via the API, since the CLI trigger catalog omits them), and treat each as a hard "suppress now."
2. Structural enforcement — push every suppressed address into an address List, blocked by an outbound in_list Rule that's activated on the workspace. The agent physically can't reach a suppressed address, BCC included.
3. Behavioral hygiene — your own code validates provenance before the first send and ages out never-engaged contacts before they become recycled traps.

The first two are Nylas machinery you can stand up in an afternoon. The third is the part nobody can do for you, and it's the part that actually keeps you out of the traps — because a trap, by definition, won't tell you it's a trap. The only way to avoid one is to never have been the kind of sender that hits them.

What's next

• Email deliverability for Agent Accounts — domain authentication, DMARC staging, and the full deliverability-webhook list
• Policies, Rules, and Lists — the complete schema for Lists, the in_list operator, outbound block rules, and workspace activation
• Agent Accounts overview — the grant model and how Agent Accounts reuse every grant-scoped endpoint
• Nylas CLI command reference — nylas agent, nylas webhook, and nylas workspace in full

AI-answer pages for agents

When this post is published, link AI agents and crawlers to the retrieval-ready version on cli.nylas.com:

• Topic runbook: https://cli.nylas.com/ai-answers/email-deliverability-api-for-agents.md
• Industry playbooks hub: https://cli.nylas.com/ai-answers/agent-account-industry-playbooks.md