Is an email marketing tool useful if users must connect their own SMTP provider?

Hi! Yes—an email marketing tool can absolutely be practical with a “bring your own sending” (BYOS) model, but it’s a very different product category than the typical all-in-one ESP. It tends to appeal most to teams that already have a sending provider they trust (or strict compliance/security needs), while many mainstream marketers still expect the platform to handle sending + deliverability end-to-end because it removes a lot of complexity and finger-pointing when things go wrong.

A good way to think about it: BYOS can be a strong fit if your platform is clearly the “campaign/automation brain” and the user’s SMTP provider is the “delivery pipe”—but you’ll need to make the pipe feel as turnkey and observable as possible.

The biggest practical drawbacks (what users will complain about)

1. “Who’s responsible for deliverability?” confusion
   When open rates drop, messages hit the spam folder, or bounces spike, customers won’t care that sending is outsourced—they’ll still ask you to fix it. If you can’t see what’s happening (or can’t influence it), support gets painful.

2. Workspace email accounts are a trap for marketing use
   A Google Workspace or Microsoft 365 mailbox SMTP is usually not appropriate for bulk newsletters/automations at scale. Limits, throttling, policy restrictions, and reputation risks show up fast. Users will try it anyway unless you steer them hard toward a real email delivery service.

3. Provider limitations break “marketing expectations”
   Marketers expect things like fast sends to large segments, reliable unsubscribe handling, suppression lists, bounce classification, and consistent tracking. A generic SMTP connection often doesn’t give you enough event data to power those expectations.

4. Inconsistent features across providers
   If you support “any SMTP,” you’ll end up with wildly different capabilities depending on whether the user connects a full email API provider (great) vs. bare SMTP (limited). That fragmentation can make your product feel unreliable unless you define clear tiers (“SMTP basic” vs “Full event-enabled providers”).

5. Compliance and consent workflows get harder
   Things like unsubscribe, opt-in records, suppression, and complaint handling still need to be airtight in your app—even if sending happens elsewhere. If your model accidentally enables people to send without proper consent, you’ll attract the wrong users and risk getting blocked by providers or inbound abuse complaints.

Must-have features if sending is third-party

If you want BYOS to feel “real” to marketers (not a developer tool), these are the features that matter most:

• Deep provider integrations (beyond SMTP) for events: bounces, complaints, delivered, deferred, opens/clicks (if you offer tracking), unsubscribes. Ideally via webhooks/event streams so automations and reporting are accurate.
• A strong suppression system: global and per-audience suppression lists, bounce-based suppression, complaint-based suppression, and “never email again” handling that can’t be bypassed by a misconfigured automation.
• Built-in unsubscribe + List-Unsubscribe support: one-click unsubscribe support is increasingly expected; at minimum, your unsubscribe must be automatic, immediate, and tamper-proof.
• Domain/authentication guidance inside the product: clear setup checks for SPF/DKIM/DMARC alignment (and warnings when misconfigured). Even if you can’t configure DNS for them, you can validate and explain the impact on deliverability.
• Sending controls: throttling, pacing, quiet hours, time zone sending, and retry rules. Third-party providers often rate-limit; your scheduler needs to handle deferrals gracefully.
• Bounce/complaint visibility and alerting: dashboards + alerts when bounce rates spike, complaint signals appear, or a provider starts deferring messages. Marketers want to know “what changed?” quickly.
• A/B testing and segmentation that remain accurate even with external sending: if tracking/events are partial, be honest in UI and reporting. Nothing kills trust like “phantom” open rates.
• Migration and deliverability guardrails: warm-up guidance (especially if users bring a fresh domain), list hygiene tools, and clear rules around purchased/scraped lists (you’ll want to prohibit them).
• Clear identity model: per-brand/from-domain management, multiple sending connections, and permissioning so agencies/teams can’t accidentally cross-contaminate reputations.

Product positioning that tends to work best

BYOS works best when you don’t market it as “an ESP replacement for everyone.” It’s usually strongest as one of these:

• “Automation + campaign builder that plugs into your existing delivery stack” (great for SaaS companies already using a provider)
• “Compliance-first / data-control-first email marketing” (some orgs prefer owning the sending relationship and logs)
• “Agency/multi-brand orchestration layer” (many clients, many senders, one place to build and manage)

A practical recommendation

If you pursue this, I’d strongly consider supporting a small number of first-class sending providers (with full event webhooks and suppression sync) and offering “generic SMTP” as a limited fallback. Marketers will be happiest when reporting, deliverability signals, and automations work consistently—and that’s much easier when you can rely on richer provider APIs rather than raw SMTP alone.

If you tell me who your ideal customer is (solo creator, SMB ecommerce, B2B SaaS, agency, enterprise) and whether you plan to support “newsletter sends” at scale vs. mostly lifecycle automations, I can suggest the cleanest BYOS approach and the minimum integration set to make it feel solid.