SMTP relay for application mail
Standard SMTP authentication. Your code points at our servers, mail goes out. No application rewrite, no proprietary SDK, no lock-in.
Free up to 1,000 emails/month · No credit card · Running since 2014
Outbound SMTP.
The relay your application deserves.
Your application needs to send mail. Password resets. Receipts. System notifications. The kind of email that has to land in the inbox or somebody can't log in. Outbound SMTP is the relay that handles reputation, throttling, and routing as the platform's job, not yours. Running since 2014.
Delivered
99.99%
last 24h
Throughput
2.1M
msgs/day
Queue
0
backlog
smtp tail us-east-1
14:02:11 250 2.0.0 OK smtp.gmail.com
14:02:11 250 queued as 04F7A3 outlook.com
14:02:10 250 accepted aspmx.l.google.com
14:02:10 250 delivered, dkim=pass mx.protonmail.ch
14:02:09 250 2.0.0 inbox apple-mx.icloud.com
14:02:09 250 accepted smtp.fastmail.com
operating since 2014 reputation: green
The path that brings people here
SMTP relay for application mail is its own category
You start with Gmail SMTP. It rate-limits you the moment a script tries to send more than a trickle.
You move to a shared cloud-provider sending pool. The mail goes out, but your messages start landing in spam because the IP reputation is shared across thousands of senders and your traffic looks indistinguishable from every other startup on the same pool. Your sender reputation becomes a side effect of whoever you happen to share an IP with.
Then you realize that "SMTP relay for application mail" is a different category than "Gmail-the-mailbox" or "shared cloud-provider sending." You need a relay that handles reputation, throttling, and routing as the platform's job, not yours.
Outbound SMTP is that relay. Running since 2014, with reputation, throttling, and routing handled inside the platform so your application doesn't have to.
FREE TIER
Free up to 1,000 emails per month
The first 1,000 emails per month are free. No credit card required to start. When your sending volume outgrows the free tier, you pay. The same expert team picks up the phone either way.
The free tier exists because we'd rather you become a customer at zero cost and let us help with whatever email problem comes up next, than gate the relationship behind a procurement conversation. As your needs grow, the relationship grows with them.
What it does
The relay layer, fully operated
Six things you don't have to build, run, or maintain because the platform does them for you.
Reputation handled inside the platform
Sending IPs are pooled and managed. Bad senders get isolated. Good senders benefit from collective reputation built over more than a decade of running relay at scale.
Throttling and queuing
Bursts are handled gracefully. No "your script tried to send 500 emails in a minute, all of them rejected" surprises. The relay absorbs spikes so your application doesn't have to.
Routing intelligence
Mail gets through more reliably to specific receivers (Gmail, Microsoft 365, big corporate gateways) because the routing path has been tuned over years of operating SMTP relay at production scale.
Sub-account and multi-tenant support
For platforms sending on behalf of customers, sub-accounts let you isolate reputation and reporting per tenant. One parent account, many isolated sending identities.
Detailed delivery logs and APIs
SMTP-level visibility into deliveries, bounces, and rejections. Exposed via API so you can pipe it into your own dashboards, alerting, or per-customer reporting.
Who this is for
Built for these sending patterns
- SaaS applications sending transactional email at any volume, from indie launches up to enterprise platforms
- Hosting providers and platforms that send mail on behalf of customers and need sub-account isolation
- Operations teams running on-premise infrastructure that need an outbound relay rather than running their own postfix-plus-reputation problem
- Developers who would rather start free and grow into paid pricing than fill out a sales form
- Existing DuoCircle customers consolidating delivery onto a stack where the same expert team supports every product
When to look elsewhere
We're not the right answer if
You need an HTTP-first developer API. The same delivery infrastructure powers our Developer Email API (unsent.dev). Same stack underneath, different shape on top. If your team prefers a clean HTTP interface to configuring SMTP servers, that's the door to use.
You need cold outreach campaigns with multi-step sequences and AI personalization. That's a different architecture. Cold outreach belongs on the sender's own mailboxes for reputation reasons. See Cold Email Outreach (NuReply, bring-your-own-mailbox).
You need a marketing-campaign platform with templates, list management, segmentation, and visual editors. That's a marketing-email category, not a relay category. Outbound SMTP is the pipe, not the campaign tool.
For the broader picture of how Outbound SMTP fits next to the rest of our delivery products, see Deliver.
What you get when you call
A real expert, not an SDR
When you contact us about Outbound SMTP, you talk to an expert who has actually run SMTP relay at scale, not an SDR working from a script. We tell you whether the relay fits your use case, whether the free tier covers your volume, and what the upgrade path looks like.
Reference calls with existing Outbound SMTP customers are available on request. Become a customer at the free tier and let's see what else we can help with.
Talk to an expert about your sending pattern
Same-day response. Real expert on the call. Become a customer at the free tier and we'll help with whatever email problem comes up next.