--- title: "Deliver: DuoCircle Email Delivery Products" description: "DuoCircle" image: "https://www.duocircle.com/images/og-default.png" canonical: "https://www.duocircle.com/products/deliver/" --- Outbound SMTP since 2014 · 1,000 emails/month free · BYO-mailbox cold outreach # Deliver. Sent isn't the same as delivered. Mail can leave your application, hit the recipient's mail server, get accepted at the SMTP layer, and still end up in spam. The path from application to inbox runs through DNS records, sender reputation, content filters, authentication checks, and platform-specific quirks. These products handle the whole path. [ Talk to an Expert → ](/contact/) [ See the products ](#products) Outbound SMTP · relay-us-east-1 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 4 sending patterns active reputation: green What's in this group ## Four products, four sending patterns [ 01 Outbound SMTP DuoCircle's flagship SMTP relay since 2014\. Reputation, throttling, and routing handled inside the platform. 1,000 emails per month free, no credit card required. Learn more → ](/email/outbound-smtp/)[ 02 Developer Email API (unsent.dev) HTTP-first email API for developers who want a clean interface instead of configuring SMTP servers. Built on the same delivery infrastructure as Outbound SMTP. Learn more → ](/email/developer-email-api/)[ 03 Inbox Placement Testing (InboxIssue) Test against real corporate mailboxes (Microsoft 365 and Google Workspace business plans with full security stacks enabled), not consumer seed accounts. API-first. Learn more → ](/email/inbox-placement-testing/)[ 04 Cold Email Outreach (NuReply) Bring-your-own-mailbox cold outreach. Connect your existing Google Workspace, Microsoft 365, or SMTP accounts; NuReply orchestrates campaigns through your own mailboxes. Your domains, your reputation. Learn more → ](/email/cold-email-outreach/) How they work together ## Different patterns. Different architectures. Different sending patterns need different architectures. Transactional mail (password resets, receipts, system notifications) belongs on dedicated relay infrastructure where reputation, throttling, and routing are the platform's problem. That's Outbound SMTP and unsent.dev. Cold outreach belongs on the sender's _own_ mailboxes so reputation builds on the sender's own domains. That's NuReply's bring-your-own-mailbox architecture, deliberately not a shared relay. The connecting tissue across all of it is deliverability visibility. InboxIssue sits beside the others as the test layer: pre-flight your transactional templates, validate cold-outreach inboxing, gate your CI on placement regressions before customers see broken mail. Same engineering team across the lineup. When an inbox-placement issue shows up that crosses two products, the team that owns one of them owns the other. Who these products are for ## The audience - Application developers sending transactional email at any volume, from indie SaaS to enterprise platforms - Operations teams running their own SMTP infrastructure who want a relay that handles reputation and throttling without a six-figure contract - Email-deliverability-conscious senders who have been bitten once by an inbox placement issue and aren't going to be bitten twice - Sales teams running cold outreach who want a tool that respects their domain reputation rather than relaying through a shared pool - Engineering teams wiring deliverability checks into CI to pre-flight transactional sends before they hit production When to look elsewhere ## We're not the right answer if **You're a high-volume, dedicated cold-outreach organization** with a stack already wired together (CRM, intent data, multi-channel orchestration). Specialist outreach platforms in that lane will fit your workflow better than NuReply. **You need a battle-hardened transactional API with a long public track record** and a giant SDK matrix. The established names in transactional email have those; unsent.dev is earlier in its public arc. **Your traffic is purely consumer (Gmail/Yahoo)** and you don't care about corporate placement. Simpler delivery and testing tools may fit your needs. ## Talk to an expert about your delivery setup Same-day response. Real expert on the call. We tell you which product fits the sending pattern. [Talk to an Expert→](/contact/) ```json {"@context":"https://schema.org","@type":"Organization","name":"DuoCircle LLC","url":"https://www.duocircle.com","logo":{"@type":"ImageObject","url":"https://www.duocircle.com/images/duocircle-logo.png"},"description":"DuoCircle is a portfolio of specialized email products covering protection, authentication, delivery, and routing. 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