Queues one email. The response is immediate; delivery happens in the background and is reported through GET /transactional/emails/{id} and your webhook.

Idempotency. Send an Idempotency-Key header (1 to 256 characters) to make retries safe. Within 24 hours, the same key with the same body returns the original message (with an idempotent-replayed: true header); the same key with a different body is a 409 invalid_idempotent_request.

Sandbox. Send from [email protected] with no DNS setup. It delivers only to your own account email and to the four test addresses. Test addresses never reach a mailbox and never count toward your limits; each one synthesizes an outcome so you can exercise your integration: [email protected], [email protected], [email protected], [email protected].

Limits. Transactional email has no quota of its own: every address in to, cc and bcc counts as one send against your SendFox plan, the same monthly sends your campaigns use, with no daily cap. When the plan has a cap, every response carries x-sendfox-sends-remaining, the sends left across campaigns and transactional email; a plan without an enforced cap sends no header. Past the cap, sends are refused with 429 monthly_quota_exceeded carrying remaining and requested. Each message holds at most 10 addresses across to, cc and bcc, at most 2 in bcc. Requests are limited to 5 per second and 300 per minute per key.

Custom headers. Pass headers to add list-management and threading headers. For one-click unsubscribe (RFC 8058, which Gmail and Yahoo require of bulk senders) send List-Unsubscribe with an https: URL in angle brackets and List-Unsubscribe-Post set to List-Unsubscribe=One-Click; the URL must accept a POST whose body is List-Unsubscribe=One-Click and unsubscribe the recipient without any further click. See the headers field for what is allowed.

Newest first. Standard SendFox paginator; bodies are never included.

Queues up to 100 emails in one request and reports a result per item. Items are independent: one invalid address, unverified sender or suppressed recipient is reported at its index and the rest are queued. The response is 200 whenever the batch itself was accepted, even if every item was refused; read each entry's error.

Limits. The whole batch's sends (one per to, cc and bcc address across every item) are reserved against your plan before any item is looked at. A batch that does not fit is refused with 429 monthly_quota_exceeded and nothing is sent, so a retry can never half-send. Sends for refused items, test addresses and replays are returned. A batch request counts as one request against the 5 per second and 300 per minute rate limit; the plan's sends are what bound volume.

Idempotency. Two levels. An Idempotency-Key header makes the whole batch replayable for 24 hours: the same key with the same emails returns the original results with idempotent-replayed: true; a different body is a 409 invalid_idempotent_request. A per-item idempotency_key protects each email on its own, exactly like the header on POST /transactional/emails, and is the one to rely on when your retry may be built from a different batch.

Sandbox, test addresses and tags work per item as on the single route.

The message without its bodies, plus its event timeline.

Returns a paginated list of contacts (100 per page by default, up to 1000 via per_page).

Supports engagement filtering through filter[...] query parameters, so you can answer questions like "who last opened over a year ago" without paging the whole account. All filter conditions are AND-ed. Pass count_only=true to get just the number of matches — the cheapest way to size an audience before acting on it.

Update contact details including name, list memberships, and custom fields

Soft-deletes a contact and cancels any scheduled deliverables

Returns paginated email deliverables and contact-level engagement summary

Import up to 1,000 contacts in a single request. Creates new contacts or updates existing ones.

Queues one action against every contact the filter matches, applied in chunks in the background. Returns immediately with an id to poll.

Run with dry_run: true first. A dry run reports how many contacts match and changes nothing — it is the only way to catch a filter that matches more than intended, and a bulk write is not undoable. An empty filter (which would match the whole account) is rejected unless it is a dry run.

Per-campaign conditions (opened_campaign_id, not_opened_campaign_id, clicked_campaign_id) are available here but not on GET /contacts, because they are resolved in the background rather than inside a request.

Bulk delete and bulk unsubscribe are deliberately not offered.

Because in_list_ids matches only subscribed members, remove_from_list with filter.in_list_ids set to that same list leaves the memberships of people who unsubscribed from it in place. They already receive nothing from that list.

tag_ids behaves the same way, so remove_tag with filter.tag_ids set to that same tag leaves the tag on people who unsubscribed from it. They already receive nothing sent to that tag. To reach every carrier regardless of opt-out status, select them by some other filter, or read them from the tag endpoints.

For a dry run, matched_count is the answer and nothing was modified. A run whose match set exceeds the per-request ceiling fails without applying anything.

Returns a paginated list of campaigns (100 per page)

Creates a campaign as a draft. To send it, use the send endpoint or provide scheduled_at. Subject lines cannot start with "RE:" or "FWD:". At least one list is required if scheduled_at is provided.

Returns stored counts and rates for one to 100 distinct owned campaigns in request order. The entire request fails with the same validation error for missing, deleted or foreign IDs. Does not return link stats or query individual delivery events.

Only draft campaigns (not yet sent) can be updated. All fields are optional.

Only draft campaigns (not yet sent) can be deleted. Uses soft delete.

Schedules a draft campaign for immediate sending. The campaign must:

• Not already be sent or scheduled
• Have at least one list assigned
• Not be a confirmation (double opt-in) email — those are delivered to each contact as they subscribe, never as a broadcast
• The user must not be in a warmup/throttle period

All existing abuse prevention applies automatically: content approval workflow, sending throttles, spam detection, and bounce rate monitoring.

Delivers the rendered campaign to the addresses given so it can be checked in a real inbox. This is a real send to those addresses only: the campaign's audience is untouched and the campaign stays a draft. Recipients are added to the account's "My Test Contacts" list.

Limits: up to 30 addresses per call (1 on the free plan) and 30 test sends per account per day, shared with Send Test in the SendFox app. A test from a newly created account goes to the account's own address only, unless the campaign sends from a domain the account has verified; notice in the response says so when addresses were dropped.

Returns sent count and open/click/bounce/unsubscribe/spam counts and rates, all read from stored counters.

Pass include_link_stats=true to also get link_stats — the campaign's links ranked by click count. That part is opt-in because it counts rows in email_link_clicks once per link rather than reading a counter, so leaving it off keeps this endpoint as cheap as it has always been.

Returns the contacts in one of a sent campaign's engagement groups. non_openers covers contacts the campaign actually sent to who did not open it — queued and cancelled deliverables are excluded, since they never had the chance.

Creates a new draft with the original's content, sender, and exclusions, aimed at the chosen slice of the original audience. Omit scheduled_at to leave it as a draft. The source campaign's lists are deliberately not carried over — the engagement segment is the audience.

Returns list details including average open and click rates

Soft-deletes a list. Returns 409 if the list is used by forms, landing pages, or automations.