--- title: "Mail Flow Monitoring: Free round-trip SMTP and IMAP monitoring since 2018 | DuoCircle" description: "Round-trip SMTP and IMAP monitoring with multi-channel alerts (email, SMS, webhook, PagerDuty, Slack). Free, continuously running since 2018. Real round-trip tests, not synthetic pings. The community tool we maintain because watching mail flow should not require an enterprise budget." image: "https://www.duocircle.com/images/og-default.png" canonical: "https://www.duocircle.com/email/mail-flow-monitoring/" --- Free since 2018 · Real round-trip tests · Email, SMS, webhook, PagerDuty, Slack # Mail Flow Monitoring. Find out before your users do. Email is one of the few systems most organizations notice only when it stops working. By the time someone files a ticket, the damage is already in someone's day. Mail Flow Monitoring is the free tool we built and have maintained since 2018 to surface that failure before the customer ticket does. Real round-trip SMTP and IMAP tests, configurable thresholds, alerts wired into your existing pager rotation. [ Talk to an Expert → ](/contact/) [ Visit mailflowmonitoring.com ](https://mailflowmonitoring.com/?utm%5Fsource=duocircle&utm%5Fmedium=capability&utm%5Fcampaign=cross%5Fsell) Free, no credit card No signup gauntlet Mail Flow Monitoring · widgets.com Uptime 100% last 30 days Round-trip 2.1s avg, last hour Probes 2,880 today Round-trip latency, last 24hp95: 3.4s probe log every 30s 14:02:11 \[smtp\] delivered + read 2.1s 14:01:41 \[imap\] fetched probe-msg 340ms 14:01:11 \[smtp\] delivered + read 1.9s 14:00:41 \[imap\] fetched probe-msg 280ms 5 alert channels armed all probes green FREE SINCE 2018 ## Free, full stop. Not a trial. DuoCircle's origin charter is to take care of every customer who comes our way. Mail Flow Monitoring is the version of that promise we extend to the broader email community, including organizations that are not customers and may never become customers. If your email infrastructure goes dark, the cost of a missed reply hits you the same as it hits anyone bigger. Enterprise monitoring tools cost what they cost. We built this so visibility into your mail flow does not require a procurement conversation. Maintained by the same team that runs the rest of the portfolio. Kept up to date. Not bait for an upsell. Use it. [Sign up free at mailflowmonitoring.com ](https://mailflowmonitoring.com/?utm%5Fsource=duocircle&utm%5Fmedium=capability&utm%5Fcampaign=cross%5Fsell) What it watches ## Real tests, real alerts, real signal A round-trip SMTP and IMAP test, configurable thresholds, multi-channel alerts, and the kind of failure-mode coverage you only get when the platform is sending real mail through your real path. 01 ### Real round-trip SMTP and IMAP tests Not a synthetic ping or a port check. The platform sends a real message through your SMTP path, watches it travel through your routing, and confirms it lands in the destination mailbox via IMAP. Full headers, full transaction logging, and a true end-to-end verdict on whether your mail flow is actually working. 02 ### Configurable thresholds and intervals A low-volume domain may want hourly checks. A transactional-mail platform might want sub-minute resolution. Tune timeouts and check frequency to your environment so the alerts you receive are signal rather than noise. 03 ### Multi-channel alerting When the round-trip fails or the timing breaches your threshold, the alert goes where your team actually lives. Email, SMS, webhook, PagerDuty, and Slack are all supported out of the box. Wire it into the pager rotation that already exists rather than building a new escalation surface. 04 ### Catches silent spam-filter delays Some failure modes do not bounce. Mail goes in, gets greylisted or quietly held, and arrives an hour late. The round-trip timing surfaces those cases the way a port check never will, because the platform is measuring the actual time from send to delivery rather than whether port 25 answered. 05 ### Validates the full path, not just the endpoint MX records, SMTP servers and relay software, the upstream internet link for self-hosted infrastructure, spam-filter behavior on the path, and the final IMAP delivery. Any of those breaking would silently degrade your mail flow without an obvious external symptom. The round-trip catches all of them. 06 ### Free since 2018 No signup gauntlet, no credit card, no upsell path. Mail Flow Monitoring is the version of our origin charter ("take care of every customer who comes our way") extended to organizations that may never become paying customers. We have run it continuously since 2018 because email-flow visibility should not require an enterprise budget. Who this is for ## The audience - Solo IT admins and small operations teams who run their own SMTP infrastructure and want a webhook to fire before the customer ticket does - Mid-market mail teams managing hybrid Microsoft 365, Exchange, or co-located mail flow where any link in the path could quietly break - Hosting providers and platforms that send transactional mail on behalf of customers and need round-trip verification on the relay path - Anyone running self-hosted or co-located mail infrastructure where the upstream internet link, the relay software, and the spam filter all live in different blast radii - Existing DuoCircle customers who want round-trip telemetry alongside the rest of the portfolio Mail Flow Monitoring is part of the broader [Authenticate](/products/authenticate/) group, alongside [DMARC Report](/email/dmarc/) and [SPF Management (AutoSPF)](/email/spf-management/). Authentication tells receivers your domain is the real one. Monitoring tells you whether the path your mail takes is still working. When to look elsewhere ## We are not the right answer if **You need a full enterprise email observability suite** with SIEM and SOC integration, retention dashboards, and per-tenant analytics. Mail Flow Monitoring does one thing well, round-trip mail flow tests with alerting. It is not the right shape for a security-operations tooling line item. **You need application-layer email diagnostics** like open rates, click tracking, or deliverability scoring at the inbox level. That is a marketing-email observability category, not a mail-flow monitoring category. Different problem, different tool. **You need DMARC monitoring or aggregate reporting.** Different layer. See [DMARC Report](/email/dmarc/) for that part of the authentication picture. Mail Flow Monitoring tests that mail flows; DMARC Report tells you whether the senders are who they claim to be. **You need authentication setup help.** Mail Flow Monitoring confirms that mail moves; it does not validate whether SPF, DKIM, and DMARC are correctly configured. [SPF Management](/email/spf-management/) handles the SPF side of that question. What you get when you call ## An expert on the call, not an SDR working from a script The product itself is free and self-serve. Sign up at [mailflowmonitoring.com](https://mailflowmonitoring.com/?utm%5Fsource=duocircle&utm%5Fmedium=capability&utm%5Fcampaign=cross%5Fsell) and you have monitoring running in minutes. Talk to us when you have a complex monitoring setup, want to discuss integration with a specific incident-response stack, or are running self-hosted infrastructure where the round-trip test path needs custom configuration. The person on the call is the person who has actually run mail-flow monitoring at production scale, not an SDR working from a script. Same expert team that supports the rest of the portfolio. No signup gauntlet, no upsell, no procurement runaround. ## Sign up free, or call us about a complex setup Same-day response. Real expert on the call. The tool itself is free and self-serve; the call is for the cases where it gets interesting. [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. We deliver about 90% of category-leader capability at roughly half the price, backed by experts who own the outcome. 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