Sendloop SMTP Settings and Configuration (2026)

The honest answer to “Sendloop SMTP settings” has two halves. There is no relay to point Postfix, a WordPress plugin or a Django backend at. But what most people are really after, an SPF include and a DKIM record so campaigns authenticate, does exist and is set out in full below. If you need a genuine relay, the platforms that publish one include Brevo, Mailjet, Postmark, Amazon SES and SMTP2GO. Among Sendloop’s peers, Sender, Moosend, MailerLite and EmailOctopus are the campaign tools worth comparing here.

Quick reference

Why Sendloop has no SMTP relay

Sendloop is a campaign ESP, not a mail infrastructure vendor. Its architecture assumes you compose in its web app or push subscribers over its HTTP API, then let Sendloop decide when and how the mail leaves. An SMTP relay is the opposite posture: your application owns the sending decision and the provider only accepts and delivers. Sendloop was never built around that hand-off, and its parent company makes the split explicit. Octeth’s self-hosted Email Platform is marketed as routing through Amazon SES, SendGrid, PowerMTA, KumoMTA or your own Postfix box. Octeth consumes relays; it does not sell one. Sendloop inherits that position.

One historical wrinkle explains most of the confusion. On December 9, 2016 Sendloop announced a “Transaction Email Gateway” and wrote that customers could send system email through it “via API or SMTP access.” That is the only official statement that Sendloop SMTP ever existed. It pointed to gateway documentation on help.sendloop.com, which today resolves solely to 100::-the RFC 6666 discard-only block, deliberately routed nowhere, while its stated replacement, a Notion page linked from Sendloop’s own help-portal URL, renders blank. Whether the gateway was retired or merely undocumented cannot be established officially. The practical outcome for 2026 is identical either way: no supported, published way to configure an SMTP relay against Sendloop, and no current plan that sells one.

What you actually need instead

Sending transactional email

Password resets, receipts and alerts need a relay that publishes an SLA, a hostname and a status page. Sendloop has none of the three. Use Postmark when transactional inbox placement is the priority, Amazon SES for the lowest per-message cost if you already run on AWS, or SMTP2GO when legacy software has to be pointed somewhere simple. All three publish a hostname, ports 587 and 465, and rotatable credentials. Keep Sendloop, if at all, for campaigns only.

Connecting a CMS or app

WordPress SMTP plugins, Laravel’s mail driver, Action Mailer and Django’s EMAIL_HOST all expect host, port, username and password. There is nothing to enter for Sendloop, and smtp.sendloop.com resolving is not the exception it looks like, see the mistakes below. Configure the CMS against a real relay such as Brevo or Mailjet, then connect Sendloop separately over Zapier or its API if you still want subscribers synced.

Routing internal notifications

Cron output, monitoring alerts, CI failures and form submissions are the classic reason people hunt for an SMTP host. They are low volume and latency-tolerant, so any relay with a usable free tier will do. Point the notifier at it and leave Sendloop out of the path: routing operational alerts through a marketing ESP mixes two reputations that should stay apart, and on the Free plan it is not even viable at $0.01 per email.

Sending domain authentication

This is what most visitors actually came for. Authenticating your domain is what makes Sendloop campaigns arrive as you@yourdomain.com and pass SPF and DKIM at Gmail, Outlook and Yahoo. It lives under Settings › Sender Domain Authentication and requires a dedicated sender domain, a Pro feature at $39/mo, unavailable on the Free tier.

SPF and DKIM setup

Open Settings › Sender Domain Authentication, click Authenticate Sender Domain and enter your domain. The Domain Control Panel then shows the exact records to publish. Add them at your DNS host and click Check DNS Records. Sendloop’s guide warns that propagation can take several hours, so if verification fails on the first attempt, wait and re-check rather than re-generating the records.

; 1. SPF, merge into your ONE existing SPF record.
;    Never publish a second SPF TXT record on the same host.
example.com.               TXT    "v=spf1 include:sendloop-1.com ~all"

; With another sender already present, combine the includes:
example.com.               TXT    "v=spf1 include:sendloop-1.com include:_spf.google.com ~all"

; 2. DKIM, the selector is hardcoded to "sl".
;    The p= value is generated per domain in your Domain Control Panel.
sl._domainkey.example.com. TXT    "v=DKIM1; k=rsa; p=<public key shown in your Domain Control Panel>"

; 3. OPTIONAL, branded link aliasing for click-tracked URLs.
links.example.com.         CNAME  <target supplied by the Domain Control Panel>

Two details matter. The selector is fixed at sl, so there is exactly one Sendloop DKIM key per domain, two Sendloop configurations, or a Sendloop and an Octeth configuration, cannot coexist on one domain without colliding. And the p= value is unique to your account: it is never a shared string copied from a guide, including this one.

DMARC alignment

Sendloop publishes no DMARC guidance at all. Its authentication guide covers SPF, DKIM and the link-alias CNAME and never mentions DMARC or alignment, despite Gmail and Yahoo requiring a DMARC record from bulk senders since February 2024. That is a documentation gap, not a technical limit: the SPF include and the sl._domainkey record both sit on your own domain, so both authenticate in alignment with a From: address there. p=quarantine or p=reject is achievable, you just author the record yourself.

; Start in monitoring mode and read the aggregate reports first.
_dmarc.example.com.  TXT  "v=DMARC1; p=none; rua=mailto:dmarc@example.com; adkim=r; aspf=r; pct=100"

; Tighten only once reports show Sendloop and every other sender passing.
_dmarc.example.com.  TXT  "v=DMARC1; p=quarantine; rua=mailto:dmarc@example.com; pct=100"

Stay at p=none for at least two reporting cycles. If you pair Sendloop with a separate relay, both senders must show passing and aligned in your aggregates before you move to p=quarantine, or you will quarantine your own receipts.

Sending limits

Sendloop publishes no throughput documentation. Its plans meter subscribers stored, not messages per hour, and the help portal that would have carried operational numbers is offline. Every figure below is marked unpublished rather than estimated, an estimate here would be a guess dressed as a fact.

Common mistakes

Pairing Sendloop with an SMTP provider

The recommended setup

Split the streams by purpose. Sendloop keeps the marketing campaigns it was designed for; a dedicated relay-Postmark, Amazon SES, Brevo or SMTP2GO-takes everything your application generates. Use a subdomain split so reputations stay independent: campaigns from news.example.com, application mail from mail.example.com, each with its own DKIM key and SPF record. A bad campaign then cannot depress delivery of your password resets, and each stream reports separately in DMARC aggregates.

Weigh the trade-off honestly: two vendors, two DNS configurations and two bills, for a platform whose blog has been silent since May 2023, whose documentation is offline, and whose only official SDK shipped in 2015. With lists and automations already in place, pairing is reasonable. For a new project, moving the campaigns to MailerLite, Sender, Moosend or EmailOctopus-all actively developed, several with a relay of their own, collapses the problem into one vendor.

Keeping the two systems from conflicting

Three failure modes account for nearly every problem in a paired setup. First, the double SPF record: adding a relay’s include as a second TXT record instead of merging it produces a permerror and fails SPF for both senders. Exactly one SPF record per host, containing every include, and watch the 10-lookup limit, since each include costs at least one.

Second, DKIM selector collision: Sendloop is fixed at sl, so pick a relay whose selector is configurable or distinct and confirm the records live at different hosts before publishing. Third, double-sending: when the same trigger exists as both a Sendloop automation and an application-side message, subscribers get two copies from two vendors and only one is suppression-aware. Decide per event type which system owns it, disable the duplicate, and verify against Sendloop’s webhook events rather than assuming. Throughout, hold DMARC at p=none until aggregates show both senders passing and aligned, tightening while one side is misconfigured quarantines real mail.

Frequently asked questions