What open-source email marketing tools can schedule campaigns and send OTP emails?

Hi! For scheduled newsletters/promos and reliable OTP/verification emails, the best open‑source “combo” usually looks like: use an open‑source marketing app for campaigns (Mautic or listmonk), and use a dedicated transactional sender path for OTPs (either a transactional email provider via SMTP/API, or a self‑hosted delivery platform like Postal). You can send OTPs from the marketing tool itself, but OTPs are time‑sensitive and you’ll generally get better reliability (and fewer compliance/deliverability headaches) by keeping transactional and marketing mail separated.

If you want one platform that can do both

• listmonk: Great if you want something lightweight and straightforward for newsletter sending + scheduling, and it also supports transactional templates and a transactional send API (handy for OTP/verification). It’s not a full “automation suite” like enterprise tools, but it’s fast to run and easy to integrate into an app.
• Mautic: Best when you want full marketing automation (segments, drip campaigns, lead scoring, behavioral triggers, etc.) and scheduled/broadcast campaigns. Mautic can also send “template/transactional-style” emails (for things like confirmations), but many teams still route OTP/password reset through a separate transactional pipeline for maximum reliability.

If you want best-in-class OTP reliability (recommended approach)

• Keep OTP/verification emails out of your newsletter system and send them from your application via:
  • a dedicated transactional email service (via SMTP or API), or
  • Postal (open source) if you want to self-host the delivery infrastructure and have logs/webhooks/control similar to a “SendGrid/Mailgun-like” setup.

This separation helps because OTP mail needs speed and consistency, while marketing mail needs compliance features like unsubscribe handling, preference management, and careful list hygiene.

What to look for (so deliverability stays strong)

1. Separate domains (or at least separate subdomains)

• Use something like news.yourdomain.com for marketing and mail.yourdomain.com for transactional/OTP, so a bad marketing day doesn’t tank your OTP deliverability.
• Also consider separate “From” addresses and sending identities.

1. Authentication: SPF, DKIM, DMARC (non-negotiable)

• Set up SPF + DKIM for the sending domain/subdomain you’ll use.
• Add DMARC so mailbox providers can trust your mail and you can see authentication failures (start in monitoring mode, then tighten later).

1. Bounce/complaint handling and list hygiene

• Your tool/sender should support processing bounces and complaints (webhooks or a way to ingest them).
• Automatically suppress hard bounces, repeated soft bounces, and complainers.
• Don’t import old/unverified lists; keep everything opt-in and current.

1. Unsubscribe & preferences for marketing

• For newsletters/promos: include a clear unsubscribe link, honor it quickly, and consider a preference center (reduce frequency, choose topics).
• Never try to “hide” marketing content in transactional emails to avoid unsubscribes—that’s a fast way to hurt trust and deliverability.

1. Rate limiting + warm-up

• If you’re moving from a paid ESP to self-hosted or a new sender, don’t blast your full list on day one. Ramp volume gradually and watch bounces/complaints.
• OTP emails should be low-latency; make sure your transactional path isn’t stuck behind big campaign queues.

Compliance basics (US + generally good practice)

• For email marketing, make sure you have clear opt-in/consent records, include your sender identity, and provide an easy unsubscribe (these are core expectations under laws like CAN-SPAM and also mailbox-provider policies).
• For transactional/OTP, keep the content strictly functional (verification code, expiry info, support contact). Don’t add promos or cross-sells inside OTP messages.

If you tell me roughly which matters more—advanced automation (Mautic) vs simplicity and speed (listmonk)—and whether you’re willing to self-host a mail delivery stack (Postal) or prefer using an SMTP/API sender, I can suggest a clean setup pattern for your exact use case.